Optical Temperature Sensor Research Articles

Fiber optic relative humidity and temperature sensor with the cascaded Vernier effect based on the C-shaped cavity structure

The water-absorbent sensing film, coated on the surface of traditional optical fiber humidity sensors, often suffers from detachment issues. In this paper, we present what we believe to be a new fiber-optic cascaded Fabry-Perot interferometer sensor for detecting relative humidity (RH) and temperature, without the need for sophisticated instrumentation. The sensing structure comprises two sections of single-mode optical fibers and a C-shaped cavity between them. The C-shaped cavity is created by grinding the side of a hollow-core fiber with fiber optic abrasive paper. The Vernier effect arises from the cascaded interaction between the C-shaped cavity filled with ultraviolet optical glue (NOA61) and the subsequent single-mode fiber pigtail. The sensor exhibits a high RH sensitivity of 0.248 nm/%RH (35-95%RH) and an RH resolution of up to 0.08%RH. It also has high-temperature sensitivities of -1.091 nm/°C (25 - 65°C). Furthermore, simultaneous measurement of RH and temperature is achieved by establishing a dual parameter matrix, and the sensor's response time and recovery time for RH and temperature are within 300s. Therefore, this work provides a simple and cost-effective manufacturing process and the proposed RH and temperature sensor features a compact size, strong environmental adaptability, and significant potential for practical applications.

Thermal enhanced upconversion luminescent of Sc2W3O12:Yb3+/Er3+ for optical temperature measurement

In recent years, people have higher requirements for temperature measurement with the development of optical temperature measurement. Meanwhile, the emission intensity of most fluorescent materials is quenched by thermal effects as the temperature rises, making it challenging to meet the specifications of fluorescent materials employed in the field of pyrometry. In this work, the pure phase of Yb3+/Er3+ ions co-doped Sc2W3O12 phosphor was successfully prepared. Sc2W3O12: Yb3+, Er3+ samples showed strong green emission and weak red emission. The optimal doping concentrations of Yb3+ and Er3+ ions are 0.3 and 0.02, respectively. The potential upconversion luminescence (UCL) mechanism was investigated by analyzing the UCL spectra, downshift emission spectra and power dependence spectra of Yb3+/Er3+ ions co-doped Sc2W3O12. The upconversion emission excitation path is mainly through Er3+ ions from 4I11/2 absorption photon excitation to 4F7/2 energy level, then the photons of 4F7/2 relaxes to green and red emission energy levels and returns to ground state for emitting green and red light. In addition, according to the UCL green light intensity increasing with temperature, it serves as an optical temperature sensor. The temperature sensitivity of the sample was explored in the temperature range of 298 K–673 K. This study provides new materials and ideas for non-contact temperature sensing.

Printed Optical Waveguide Temperature Sensor With Rhodamine-Doped Core

Printed Optical Waveguide Temperature Sensor With Rhodamine-Doped Core

Boltzmann thermometry: Eu3+-doped monoclinic Y2O3 and Y2O3@SiO2 nanoparticles

During last decade optical thermometry has gained considerable attention due to the possibility to determine temperature remotely in cases when traditional contact methods fail. The most widespread type of optical temperature sensors is based on monitoring luminescence intensity ratio between transition originated from thermally coupled energy levels. Eu3+ ions own the largest energy gap between thermally coupled 5D1 and 5D0 energy levels among all lanthanides, which guarantees a high thermal sensitivity of Boltzmann-type thermometry. Here, uncoated m-Y2O3:Eu3+ and core-shell m-Y2O3:Eu3+@SiO2 nanophosphors have been successfully utilized as ratiometric thermal sensors within the 298–873 K range. It was shown that the calculation method (integral or peak intensities) only slightly affects thermal sensitivity. SiO2 coating significantly enhances emission intensity and increases lifetime, but has no noticeable effect on thermal sensitivity. m-Y2O3:Eu3+ nanophosphor has the best thermometric characteristics of Sr = 0.96 % K-1 at 373K and δT = 0.5 K.

Up-Conversion Luminescence and Optical Temperature Sensing of Tb3+, Yb3+, Er3+ Doped (Gd, Y, Lu)2O2S Series Phosphors

The phase analysis, luminous intensity, and luminescence lifetime of different doping concentrations of Tb3+ (1 mol %–11 mol %), Yb3+ (9 mol %–54 mol %), Er3+ (0.1 mol %–1.1 mol %) ions and different introduction concentrations of Y3+ (1 mol %–6 mol %) and Lu3+ (0.5 mol %–3 mol %) of Gd2O2S series phosphors were studied systematically. In addition, the energy transfer model of Tb3+-Yb3+-Er3+ was established by analyzing the changes of luminous intensity and luminescence lifetime of novel (Gd, Y, Lu)2O2S phosphors co-doped Tb3+, Yb3+ and Er3+ which were prepared by the coprecipitation-high temperature solid-state reaction method. The luminescence intensity ratio equations of the sample excited by 980 nm was obtained at 313–553 K. And the absolute sensitivities were 0.0033 (313 K). This work is of reference value to the study of the mechanism of up-conversion system.

Up-Conversion Luminescence and Optical Temperature Sensing Properties of NaLuF4:Yb3+/Ho3+ Micron-Sized Crystals at Low Temperature.

Non-contact temperature sensors utilising the fluorescence intensity ratio and the unique up-conversion (UC) luminescence of rare-earth ions have numerous benefits; however, their operational temperature range has remained limited. In this study, NaLuF4:Yb3+/Ho3+ samples were prepared by the hydrothermal method. The samples exhibited exceptional UC luminescence properties at low temperatures. The intensity of the green emission (with peak wavelengths of 540 and 546 nm) gradually decreased with increasing temperature, and the green emissions showed a unique change at low temperatures. In addition, we studied the dependence of the UC luminescence intensity on the excitation power and the variation in the decay lifetime with temperature. The experiments revealed excellent luminous performance and significantly enhanced sensitivity at low temperatures; the maximum absolute sensitivity Sa and relative sensitivity Sr of the 540 and 546 nm thermally coupled energy levels were 1.02% and 0.55% K-1, respectively. The potential temperature sensing properties of Yb3+/Ho3+-co-doped NaLuF4 makes it suitable for temperature sensing applications at temperatures as low as 30 K. This study offers a novel approach for the advancement of temperature sensing technology at low temperatures.

Temperature Optical Sensor Made of Recycled Waste Materials and Implementation of Machine Learning Method to Expand Its Measurement Range

Temperature Optical Sensor Made of Recycled Waste Materials and Implementation of Machine Learning Method to Expand Its Measurement Range

Droplet temperature measurement using a fiber Bragg grating

The need to measure droplets temperature with high precision in moderate or extreme environments has driven the development of advanced methods. Here, we report, for the first time, the measurement of droplet temperature using optical fiber-based temperature sensors. Specifically, a fiber Bragg grating sensor was used as a non-invasive technique to determine the temperature behavior of single micro-volumetric pendant droplets. The fiber sensor method, which provides indirect measurements, was validated by experimental and simulation data from the literature, showing good agreement. The temperature measurements rely on monitoring the vapor layer temperature near the droplet at sub-millimeter fiber-to-droplet distances and on determining a coefficient that characterizes the temperature difference between the droplet and the surrounding vapor layer at the liquid–gas interface. We calibrated the method by conducting measurements under various relative humidities and fiber-droplet contact conditions. We found that the coefficient remains constant for a specific distance regardless of the relative humidity or the droplet volume. Furthermore, we observed the minor influences that the environmental relative humidity and droplet content has on the behavior of the recorded temperatures during the short period after droplet generation.

High sensitivity optical fiber temperature sensor based upon a polydimethylsiloxane filled Fabry-Perot interferometer

A high-sensitivity temperature sensor based upon an optical fiber Fabry-Perot interferometer (FPI) filled with polydimethylsiloxane (PDMS) is reported that employed a single mode fiber (SMF) and a hollow core fiber (HCF) to enhance the sensitivity. The sensing characteristics were investigated from 20 °C to 40 °C. The experimental results demonstrate that the sensor is sensitive to temperature due to the high thermal optical coefficient (TOC) and high thermal expansion coefficient (TEC) of PDMS, achieving a high sensitivity of 2.155 nm/°C. The designed sensor shows great potential for high-precision temperature sensing applications due to its high sensitivity, compact structure, and simple preparation.

Highly stable lead-free perovskite glass for real-time 3D surface temperature measurement across the wide temperature range

3D Optical temperature sensors are highly valuable in various fields such as industry, medicine, and aerospace, as they allow for real-time detection of temperature distribution on surfaces. However, existing temperature sensor materials face challenges in achieving accurate detection across a wide range of temperatures from low to high. To overcome these issues, Cs2Zn1-xEuxBr4 perovskite B2O3–BaF2-Ga2O3 (BBG) borate glass was prepared for non-contact 3D optical temperature sensing. Cs2Zn1-xEuxBr4 perovskite B2O3–BaF2-Ga2O3 (BBG) borate glass improves the stability, thus expanding the temperature measurement range. Utilizing the fluorescence intensity ratio (FIR) method, based on the 613 nm (Eu3+: 5D0→7F2) and 592 nm (Eu3+: 5D0→7F1) emission bands, a FIR benchmark database was constructed for the entire temperature range from 10 K to 640 K. Temperature calculation equations related to FIR were derived, with a maximal relative sensitivity of 0.08 % K−1 at 180 K. The method for measuring the surface temperature of 3D curved aircraft is based on the rare earth perovskite borate glass. The temperature measured with this method is close to the thermal imaging temperature and has a good temperature measuring effect. The temperature measurement range is wider and more advantageous than previously reported ranges. These results indicate that Cs2Zn1-xEuxBr4-BBG perovskite borate glass temperature sensors have broad application prospects in many applications.

Improvement of fiber optic sensor measurement methods for temperature and humidity measurement in microelectronic circuits

A wide range of applications such as healthcare, human comfort, agriculture, food processing and storage, and electronics manufacturing also require fast and accurate measurement of humidity and temperature. Optical fiber-based sensors have several advantages over electronic sensors, and much research has been conducted in this area in recent years. This paper describes the current trends in fiber optic temperature and humidity sensors. The evolution of optical structures aimed at humidity detection is presented, as well as a new design of an optical sensor used for this purpose. The main methods of humidity determination using fiber-optic laser reflection based on Optical fiber humidity sensor (FPI) were analyzed and experimental results were obtained. Based on temperature-sensitive strain variation, a method for temperature determination based on the specific spectral back-reflection effect of fiber Bragg gratings (FBGs) is considered. Experimental analyses were conducted on the light reflection of humidity-sensitive agarose using optical fibers based on the Fabry-Perot Interferometer (FPI). It exhibits a good linear response to relative humidity, ranging from 25 % to 95 %. During temperature measurement, the deformation changes of the Fiber Bragg Grating fibers showed excellent performance, ranging from –5 °C to 70 °C. New structures, such as resonators, are being explored to improve the resolution of fiber optic temperature and humidity sensors. In addition, recent studies on polymer optical fibers show that the sensitivity of this type of sensor has not yet been achieved. Thus, materials sensitive to humidity and temperature still need to be investigated to improve sensitivity and resolution

Ultra-sensitive temperature sensor based on PDMS filled Fabry-Perot cavity and air-bubble Fabry-Perot cavity in parallel

Highly sensitive fiber optic temperature sensors are designed and fabricated using the Vernier Effect (VE) and First-order Harmonic Vernier Effect (FHVE). The sensor comprises two Fabry-Perot cavities (F-P) in parallel. Single-mode fiber is fused together with a small segment of capillary, and then polydimethylsiloxane (PDMS) is filled in the capillary to form a sensing F-P cavity. The reference F-P cavity is composed of air-bubble inside the single-mode fiber etched by femtosecond laser. Two reference interferometers FPI1 and FPI2, as well as two sensing interferometers FPI3 and FPI4, were prepared using this method. The free spectral ranges (FSR) of FPI1, FPI2, FPI3, and FPI4 are 14.09 nm, 7.80 nm, 7.01 nm, and 6.48 nm, respectively. The temperature sensitivities of FPI3 and FPI4 are 2.2622 nm/°C and 2.4958 nm/°C, respectively. FPI1 and FPI2 are almost insensitive to temperature. FPI3 and FPI2 have similar FSR, and they generate traditional VE sensor in parallel, with a temperature sensitivity of 20.41 nm/°C, which is about 9.02 times that of FPI3. The FSR1 of FPI1 is approximately twice that of FPI3, and they generate FHVE1 in parallel. The temperature sensitivity of FHVE1 reaches −99.66 nm/°C, which is 44.05 times that of FPI3 and 4.88 times that of VE1. This is currently the highest known temperature sensitivity. In addition, the FSR1 of FPI1 is also approximately twice that of FPI4. Parallel connection between FPI4 and FPI1 can also generate FHVE2, but the sensitivity is only 22.17 nm/°C, which is 4.5 times lower than the sensitivity of FHVE1. From this, it can be seen that in FHVE, the smaller the FSR detuning (FSRr - (i+1) FSRs) between the sensing cavity and the reference cavity, the greater the amplification factor of sensitivity. The materials of the proposed sensor are cheap, easy to fabricate, and has high sensitivity. It can be used to measure temperature in environments with high sensitivity requirements.

Spectroscopic and Thermographic Qualities of Praseodymium-Doped Oxyfluorotellurite Glasses.

The thermal stability of oxyfluorotellurite glass systems, (65-x)TeO2-20ZnF2-12PbO-3Nb2O5-xPr2O3, doped with praseodymium was examined. The different concentrations of praseodymium oxide (x = 0.5 and 2 mol%) were applied to verify the thermal, optical and luminescence properties of the materials under study. The relatively high values of the Dietzel (ΔT) and Saad-Poulain (S or H') thermal stability factors determined using a differential thermal analysis (DTA) indicate the good thermal stability of the glass matrix, which gradually improves with the content of the active dopant. The temperature dependence of optical spectra in the temperature range 300-675 K for the VIS-NIR region was investigated. The involved Pr3+ optical transition intensities and relaxation dynamic of the praseodymium luminescent level were determined. The ultrashort femtosecond pulses were utilized to examine a dynamic relaxation of the praseodymium luminescent levels. Although the measured emission of the Pr3+ active ions in the studied glass encompasses the quite broad spectral region, the observed luminescence may only be attributed to 3PJ excited states. As a result, the observed decrease in the experimental lifetime for the 3P0 level along with the increasing activator content was identified as an intensification of the Pr-Pr interplay and the associated self-quenching process. The maximum relative sensitivities (Sr) estimated over a relatively wide temperature range are ~0.46% K-1 (at 300 K) for FIR (I530/I497) and 0.20% K-1 (at 600 K) for FIR (I630/I497), which seems to confirm the possibility of using investigated glasses in optical temperature sensors.

Expanding the Toolbox for Industrial Luminescent Primary Thermometry: Er3+-doped SrMoO4

We herein demonstrate the feasibility of employing strontium molybdate as host matrix for trivalent erbium ions for the developing of an optical temperature sensor operating in a wide temperature range suitable for industrial applications. This class of metal molybdate, known for its chemical and thermal capabilities, works as primary luminescent thermometer, relying on the thermally coupled levels of Er3+ arising from downshifting processes, neglecting first, the requirement of calibration curve acquisition and second, the excitation induced heating on the sample typically observed in upconverting luminescent thermometers. The synthesised primary optical thermometer displays a maximum temperature relative sensitivity of 1.13 %. K−1 and minimum temperature uncertainty and 0.09 K. These values make the performance of the Er3+-doped strontium molybdate as optical temperature sensor competitive with the existing luminescent primary thermometers, including a wide operating temperature range up to 413 K and high accuracy as main features. Moreover, it can be easily scaled up and produced due to straightforwardness and cost-effectiveness of the ceramic synthesis method, matching the requirements for its usage in industrial environments.

Multiple soliton operation in Ge2Sb2Te5 saturable absorber based fiber lasers

With the rapid development of fiber lasers, the invention of novel ultrafast modulators based on the new materials is critical for furthering basic research and practical applications of mode-locked fiber lasers. Ge2Sb2Te5 is a kind of phase-change and thermoelectric material. The fields of optical fiber temperature sensors, optical switches, and phase-change memories have all made extensive use of Ge2Sb2Te5. Nevertheless, the performance of Ge2Sb2Te5 is currently unproven in nonlinear optics and ultrafast laser applications. In this study, Ge2Sb2Te5-based saturable absorbers (SAs), were successfully prepared by depositing nanosheets on a tapered optical fiber. Conventional solitons, second-order harmonic mode-locked, and double-, triple-, quadruple-, and quintuple-pulse phenomena at different net dispersions are observed. A conventional soliton was obtained at 166 mW-987 mW with a pulse interval of 102 ns and a signal-to-noise ratio of 59 dB. At 440 mW of pump power, second-order harmonic mode-locked with a 3 dB bandwidth of 3.29 nm was obtained. The experimental results show that Ge2Sb2Te5 has a broad research prospect in designing ultrafast photonic devices in the future by virtue of its low cost, narrow bandgap, high damage threshold and high stability.

Spectral-Kinetic Characterization of YF3: Eu3+ and YF3: (Eu3+, Nd3+) Nanoparticles for Optical Temperature Sensing

Spectral-Kinetic Characterization of YF3: Eu3+ and YF3: (Eu3+, Nd3+) Nanoparticles for Optical Temperature Sensing

Ratiometric visualization fluorescence temperature sensing based on dual-lanthanide metal-organic frameworks

High-performance optical temperature sensors play an important role in various fields, and lanthanide metal-organic frameworks (Ln-MOFs) are expected to be luminescent temperature sensors due to their distinctive luminescent properties. Herein, a new three-dimensional (3D) Ln-MOF [Tb(TCA)(Phen)]·DEF (1) (H3TCA = 4,4′,4′'-nitrilotribenzoic acid, Phen = 1,10-phenanthroline, DEF= N, N-diethylformamide) is constructed with a rtl topology based on {Tb2(COO)4} secondary building units (SBUs). Meanwhile, dual-lanthanide Ln-MOFs [TbxEu1-x(TCA)(Phen)]·DEF (2-6) are also synthesized by varying the ratio of Tb3+: Eu3+ in the reaction mixture, which can be applied in practical LED applications originating from their visual luminescent color changes. Among them, 4 is an efficient ratiometric fluorescent thermometer over a wide temperature range from 283 to 393 K and has a large relative sensitivity Sr of 4.2407 % K−1 at 393 K with good repeatability. Furthermore, the emission color of 4 gradually changes from yellow (283 K) to orange-red (393 K) as temperature increases for visual colorimetric temperature measurements, which attributed to the energy transfer between Tb3+ and Eu3+ ions.

Na5Y9F32:Yb3+/Ho3+/Tm3+ up-conversion luminescent single crystals for highly sensitive optical temperature sensor

A novel non-contact optical temperature sensor with excellent performance of its adequate temperature resolution (δ(T) = 0.017 K) and exceptional relative thermal sensitivity (Sr = 1.97% K−1) was developed based on the up-conversion fluorescence intensity ratio (FIR) of Ho3+/Tm3+/Yb3+ triply incorporated Na5Y9F32 single crystal grown by Bridgman method. The up-conversion (UC) emission bands at 482 nm/669 nm/700 nm of Tm3+ and 522 nm/542 nm/653 nm of Ho3+ ions were observed upon excitation of 980 nm. The effects of Yb3+ concentration from 0.5 to 4 mol% on the UC emission of the Ho3+/ Tm3+ fixed doped Na5Y9F32 single crystal were also carried out. It has been demonstrated through the calculation of the steady-state rate equation that the intensity of UC emission is linearly heightened with the pump power, confirming the conversion mechanism. The temperature sensing performance of the Ho3+/Tm3+/Yb3+ incorporated Na5Y9F32 single crystals was explored by analyzing the FIR employing thermally coupled energy levels (TCLs) and non-thermally coupled energy levels (NTCLs). The maximum values of absolute sensitivity (Sa) and relative sensitivity (Sr) of the material are estimated to be 19.1% K−1 (323 K) and 1.97% K−1 (398 K), separately, which are far higher than those of previously reported RE3+-doped UC optical temperature sensor materials. This study shows that the transparent single crystal has the great potential as a non-contact optical thermometer, and provides a new idea for studying other highly optical sensing materials.

Study on the Effects of Organic Bonding Agent and Low-Temperature Glass Solder Process on the Performance of Compact Packaged Fiber Optic Temperature Sensors

Study on the Effects of Organic Bonding Agent and Low-Temperature Glass Solder Process on the Performance of Compact Packaged Fiber Optic Temperature Sensors

Ultra-sensitive fiber optic temperature sensor based on Vernier effect in cascading Sagnac loops integrated with PMFs

An ultra-sensitive temperature sensor was proposed and demonstrated by inserting polarization maintaing fibers (PMFs) into cascading Sagnac fiber loops. Effect of the length of PMFs in an individual Sagnac loop on the temperature sensitivity of the sensor was firstly studied. As the PMF length reduces, the sensitivity increases. In the PMFs cascade Sagnac loops, the closer the lengths of the two sections of PMFs embedded in the Sagnac loops, the wider the free spectral range, resulting stronger Vernier effect and thus higher sensitivity. The temperature sensitivity of the cascade Sagnac loops is ∼ -44.28 nm/°C, a 27-fold increase than that of an individual Sagnac loop (∼-1.64 nm/°C). This newly developed temperature sensor has the merits of simple structure, high sensitivity and easy operation, and good competitiveness in the sensing field.