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Single mode lasers, particularly red-green-blue (RGB) colors, have attracted wide attention due to their potential applications in the photonic field. Here, we realize the RGB single mode lasing in a hybrid two-dimension and three-dimension (2D–3D) hybrid microcavity (μ-cavity) with a low threshold. The hybrid 2D–3D μ-cavity consists of a polymer fiber and a microsphere. Typical RGB polymer film consisting gain materials are cladded on a fiber. To achieve single mode lasing, the polymer fiber therein serves as an excellent gain cavity to provide multiple lasing modes while the microsphere acts as a loss channel to suppress most of the lasing modes. Mode switching can be realized by adjusting the pump position. It can be attributed to the change of coupled efficiency between gain μ-cavity and loss μ-cavity. Our work will provide a platform for the rational design of nanophotonic devices and on-chip communication.

This study proposes a novel twisted and coiled polymer fiber (TCPF) actuator fabricated from a polymer-coated optical fiber. The TCPF actuator is a soft actuator that is driven by heating; the TCPF actuator in combination with a cooling system has been widely studied for applications in robotics. Sensing is a major issue in such units; in particular, temperature sensing is important for the safe usage of the TCPF. To achieve this, the electrical properties of the heating wire are typically utilized. However, this method is affected by the input voltage noise because the circuit used for actuation is the same as that used for sensing. To separate these circuits, this study developed a temperature-sensing method for the TCPF based on an optical fiber. For propagating only the heat of the polymer to the optical fiber, we embedded the optical fiber in the TCPF. This study experimentally demonstrated that the TCPF actuator fabricated using the polymer-coated optical fiber can be driven by heating. Furthermore, using the developed sensing method, we achieved temperature and force control under isometric conditions.

A simply fabricated, highly sensitive, and inexpensive optical fiber temperature sensor is reported with a Fabry–Perot (FP) microcavity of controlled length. The microcavity with controllable length is fabricated by single-mode fiber (SMF) and polydimethylsiloxane (PDMS) for temperature sensing. After the PDMS is cured, the SMF is connected to the supercontinuum light source (SCLS) and the optical spectrometer analyzer (OSA) for online observation of the reflection spectrum. The micro-displacement platform is used to pull the SMF to form an air cavity. After the air cavity is stabilized, ultraviolet (UV) activated glue is used for packaging outside the PDMS. The FP microcavity is formed by the end face of the SMF and the face of PDMS. The length of the FP microcavity can be controlled online by the micro-displacement platform to a minimum of 15 µm. The free spectral range (FSR) may reach 74.8 nm and the interference fringe contrast (IFC) is up to 19.8 dB to allow sensitive measurements across a wide temperature range. The experiments demonstrate a high temperature sensitivity of 5.388 nm/°C from 33 to 93 °C with high repeatability and linearity (R2=0.9937). Stability experiments showed that the maximum changes in wavelength and intensity are only 45 pm and 0.035 dB, respectively. It is anticipated that the easily constructed, compact, and inexpensive fiber-optic temperature sensor will be employed in practical applications.

The distributed temperature sensing (DTS) system is useful for detecting its surrounding temperature. The fiber optic DTS system offers a number of unique features for which it find useful in a num...

Water pipelines are the efficient and reliable way for water transportation. Leakage of pipelines can lead to tremendous waste of water resources and large economic loss. In this paper, a novel leakage detection method was proposed based on active thermometry and fiber Bragg grating (FBG) based quasi-distributed fiber optic temperature sensing. In this method, the thermal sensing cable was fabricated by coupling heating cable with quasi-distributed temperature sensors. The heat was introduced by the heating cable and the temperature response was measured by the quasi-distributed fiber optic temperature sensor concurrently. The leakage can be detected and located by identifying the local low values in the temperature profile along the pipelines. The feasibility of the proposed method was validated by finite element simulation and experimental investigation. Good agreement between simulation and experimental study was achieved. The results confirmed the effectiveness of the proposed method for leakage detection.

A novel high sensitivity temperature sensor based on polydimethylsiloxane (PDMS) coated the Multi-Thin-Multi mode Fiber was presented. The reliable material PDMS with higher negative thermal optical coefficient and thermal expansion coefficient was selected to improve the sensitivity of the optical fiber’s temperature sensing. A section of thin-mode fiber was connected in the middle of two multi-mode fibers, so as to form the Multi-Thin-Multi mode Fiber structure, which can make the light in the cladding better interact with the external PDMS. For the two dips of the interference spectra, the temperature sensitivities of the original fiber sensor were 47.14 pm/°C and 0.093 dB/°C. After the sensing part of the fiber was coated, its temperature sensitivities were become as 75.04 pm/°C and 0.231 dB/°C, which 1.6 and 2.5 times improved, respectively. In the temperature stability experiment, a standard deviation of the wavelength variation was established to demonstrate the good stability of the sensor.

In this paper, we demonstrate that nitride-based R/G/B micro-LEDs allow temperature sensing through a forward voltage response on both temperature and display devices. In temperature sensing, micro...

Predictive maintenance and safety assessment during the construction and operational phase are becoming more and more important in modern tunnelling. However, traditional measurement methods are often time-consuming, expensive and partially require an interruption of the tunnel traffic. In this article, we present a tunnel monitoring approach based on distributed fibre optic sensing (DFOS), which delivers hundreds of strain and temperature sensing points inside the structure and gives completely new information about the behaviour of the tunnel lining. Measurements can be performed automatically without the need of access to the tunnel and hence, monitoring can be made without disturbing the tunnel construction or operation. The developed system was installed within the shotcrete tunnel lining of a railway tunnel under construction in Austria. In addition to the critical installation process, this article discusses the main monitoring results and compares them to conventional measurements.

We present the first report on reflectometric optical fiber sensing based on mechanically induced cascaded long-period grating (LPG) structure. This method utilizes in-house designed mechanical casings and a bare fiber. When a fiber is sandwiched between the casings and pressed by tightening screws, an LPG is induced due to a photo-elastic effect. By exploiting Fresnel refection at a fiber end, a cascaded LPG structure can be implemented using a single LPG, enabling reflectometric configuration. When this sensor is subjected to external physical processes, the attenuation bands change clearly, and their shift can be used for non-destructive evaluations. We show experimentally that this sensor can measure loads of up to 10 N without producing any permanent change in the fiber properties, indicating its pressure sensing capability. We also show that this sensor can potentially measure strain and temperature. In our experiments, the strain and temperature sensitivities are 9.4 nm/% and 0.045 nm/°C, respectively.

A series of garnet-structured Li6Ca(La0.99-xYbxEr0.01)2Nb2O12 (0≤x≤0.05) phosphors were originally synthesized and examined for upconversion (UC) luminescence and optical temperature sensing under 978 nm laser excitation. It was identified that the optimal content of Yb3+ sensitizer is x=0.04 for Er3+ emission and the non-thermally coupled 2H11/2/4F9/2 energy levels of Er3+ possess a superior capability of optical thermometry, whose maximum absolute sensitivity (~15.20 × 10−3 K−1 at 523 K) is generally ~1.7-6.1 times the values reported to date for most of other UC systems.

Fiber optic distributed acoustic sensor (DAS) and distributed temperature sensor (DTS) are considerably important for many applications. It is challenging to design a hybrid DAS-DTS system using the same optical fiber because the operation principles of the two sensors are different. We here deploy the widespread standard multimode fiber (MMF) for simultaneous distributed acoustic and temperature sensing. In particular, we operate the MMF in a quasi-single-mode (QSM) state to simultaneously fulfill the functionality requirements of the DAS and DTS. The reported design offers simultaneous vibration and temperature monitoring with high accuracy. In particular, the DAS has a 12.98 dB mean signal-to-noise ratio (SNR) and the DTS offers temperature measurements with ±1 °C accuracy. This technique is significant for many industrial applications because it efficiently tackles a long-standing issue in practical implementation.

A twin-core sensor with high birefringence employing a photonic crystal fiber (PCF) is presented for simulated temperature measurements based on surface plasmon resonance (SPR). The internal wall of the central hole of the PCF is plated with gold and coated with graphene oxide (Au-GO) to develop an SPR sensing channel. The results of a numerical analysis with COMSOL Multiphysics show that the birefringence of this sensing structure can reach 0.0052. In addition, an average sensitivity of -12.695 nm/ °C can be achieved in the range of 0 °C~80 °C. Compared with uncoated GO sensors and existing sensing units, this sensor shows improved stability, sensitivity and birefringence.

In this paper, we propose the use of a dual wavelength scheme for active distributed temperature sensing based on Co2+-doped fibers. A Brillouin Optical Frequency-Domain Analysis (BOFDA) set-up, operating at 850 nm, is used to detect the temperature changes along Co2+-doped optical fibers with various absorption coefficients, while optical heating is performed through a 1550-nm optical pump. A simple model describing optical heating along the Co2+-doped fiber is introduced and experimentally validated. As a proof of concept, we demonstrate that the sensor is capable to distinguish a 1-m portion of fiber immersed into water, from a section of equal length surrounded by air.

Multiple leaks in production tubing of deep wells can be efficiently identified using fiber-optic distributed temperature measurement and thereby mitigating the health, safety and environment (HSE) risk associated with a potential well barrier failure. Further, a production log can be used to gain more insight and finalize a way ahead to resolve the issues of the well integrity. An innovative solution-driven approach was identified with fiber-optic distributed measurement playing a key role. Multiple leaks were suspected in the production system and a fiber-optic cable was run to identify possible areas of leak path. In these deep wells, after the fiber-optic data acquisition, a production log was recorded across selective depths to provide more insights on leak paths. Post identification of leak depths, a definitive decision between tubular patching and production system overhaul was decided based on combined outputs of fiber-optic, production log and tubular patch technology. Results are presented for a two-well operation. Taking an example of Well A, leaks were successfully identified at three depths using the novel operational approach. Further, operation time was reduced from three days (conventional production log measurement performed during daylight operation) to one day (combination of fiber-optic distributed temperature sensing and production log in a single run). Diagnosis of production system issues were completed in one flowing and one shut-in survey condition, thereby reducing the risk of HSE exposure with multiple flowing conditions (conventional production log measurement). Additional insight and confirmation on leaks were observed from production log data which helped identify the presence of a leak across the tubing body. This observation was substantial in deciding whether to proceed with tubing patch or replace the entire production tubing. Tubing patch technology was not satisfactorily recognized to provide well integrity across leak depths. Hence, the decision was made to replace the entire production tubing. The novel operational approach affirms the versatility of fiber-optic distributed temperature measurement in solving critical issues of operation time and reducing HSE exposure while delivering decisive information on production system issues. The paper serves as a staging area for other applications of similar nature to unlock even wider horizons for distributed temperature sensing.

A new series of CaY2–10xYb9xErxGe3O10 trigermanates (space group P21/c, Z = 4) has been synthesized using an EDTA-assisted method. Under 980 nm laser diode excitation, the samples exhibit intense upconversion luminescence corresponding to the characteristic transitions 2H9/2 → 4I15/2 (400–420 nm), 2H11/2,4S3/2 → 4I15/2 (500–600 nm) and 4F9/2 → 4I15/2 (625–725 nm) in Er3+ ions. The CaY1.5Yb0.45Er0.05Ge3O10 phosphor can be used as a good temperature sensor with high absolute and relative sensitivities Sa(max) = 0.0051 K−1 and Sr(max) = 0.0109 K−1.

In this paper, optical fibre Bragg grating (FBG) and no-core fibre (NCF) sensors have been investigated for their performance in the temperature range 30–100 °C. The change in Bragg and NCF wavelengths with temperature changes was used to determine the performance and sensitivity of the sensors. The gradient of Δ $$ \lambda_{\text{FBG}} $$ and $$ \lambda_{\text{NCF}} $$ versus temperature leads the sensitivity of the FBG and NCF sensors as 23.97 and 20.08 pm/°C, respectively.

Supramolecular self-assembly is an effective method for constructing complex ordered aggregates with specific functions by noncovalent bonding. However, silver nanoclusters (NCs) have rarely been e...

We propose and experimentally demonstrate an all-fiber Lyot filter with femtosecond laser-induced high birefringence single-mode fiber (SMF) for torsion, transverse load and temperature sensing. With the femtosecond-laser processing technique, the SMF with the birefringence of 2.81 × 10-4 is manufactured by directly writing a straight cladding stress track parallel with fiber core and employed to form an all-fiber Lyot filter for sensing application. The sensitivities of the all-fiber Lyot filter with respect to torsion, transverse load and temperature are found to be -4265.669 nm/(rad/mm), -321.004 nm/(N/mm), and 0.271 nm/°C, respectively. The experimental results are powerful proof of the excellent performance of the femtosecond laser-induced high birefringence SMF based all-fiber Lyot filter for sensing application, which not only adds significantly new and important results to the fields of optical sensing, but also develops the application fields of femtosecond-laser processing technique and all-fiber Lyot filter.

Recent waste rock pile designs have been proposed to incorporate a fine-grained layer to create a capillary barrier to prevent surface water from draining into the pile interior. This study analyses active fibre optic distributed temperature sensing (FO-DTS) as a tool to measure the effectiveness a capillary barrier system following an infiltration test. A laboratory waste rock column was built with anorthosite waste rock overlain by sand. Volumetric water content is calculated during heat cycles lasting 15 min powered at 15 W/m in the column. A new algorithm is employed to circumvent several requirements for soil specific calibration. The inferred moisture contents were verified by soil moisture probes located adjacent to the cable. The FO-DTS data indicate, at vertical resolutions up to 2 cm, that water is retained in the sand and does not drain into the anorthosite following the infiltration test. The coefficient of determination, R2, between the inferred and measured volumetric water content in the fine cover sand layer is 0.90, while the screened anorthosite maintained an R2 of 0.94 with constant moisture content throughout the test. This study will ultimately help guide future waste rock storage design initiatives incorporating fibre optic sensors, leading to improved environmental mine waste management.

This paper shots to attain automatic control solution is suggested to control the fan speed. Arduino micro controller is the heart of the circuit as it controls all the functions. The temperature sensor LM35DZ senses the temperature and converts it into an electrical signal, which is forwarded to the microcontroller. A circuit with LM35DZ temperature sensor, Arduino UNO as a main processor, and few of electronic components is designed and implemented to control the fan speed automatically. A fan speed control has been designed and constructed based on LM35DZ as the temperature sensing device. The microcontroller (MCU) ATMega8/168/328 allows dynamic and quicker control and the LCD makes the system user-friendly. Sensed temperature and fan speed levels are concurrently shown on the LCD board.

In this work, the up-conversion luminescence of Yb 3 + /Er 3 + doped Gd2O3 phosphors for optical temperature sensing in green and red regions are investigated. The intense green (522 and 562 nm) and red emissions (660 and 682 nm) radiated from Er 3 + /Yb 3 + tri-doped Gd2O3 phosphors are successfully realized via tuning the doping proportion of Er 3 + and Yb 3 + . To evaluate their potential ability of optical thermometry in green light range and the first biological window, the temperature-dependent green and red emissions are investigated. Based on the florescence intensity ratio (FIR) of 522 and 562 nm, the absolute sensing sensitivities of Gd2O3: 1 mol% Er 3 + /4 mol% Yb 3 + and Gd2O3: 1 mol% Er 3 + /6 mol% Yb 3 + phosphors reach 1.16 and 1.2% K−1 (523 K), respectively. In addition, the temperature sensing sensitivities based on the FIR of 660 and 682 nm reach 0.8 and 0.6% K−1 (300 K), respectively. Moreover, the changes of FIR ( Δ R) are smaller than 3% within the cycling heat and cool processes. These results reveal that Gd2O3:1mol%Er/4(6)mol%Yb phosphors are promising for FIR-based temperature sensing in high temperature via green emissions and room temperature via red emissions.

We demonstrated a linear-cavity fiber laser using a fiber Bragg grating (FBG) fabricated by femtosecond laser and a Sagnac loop as cavity mirrors. The temperature sensing response of the fiber laser was characterized by placing the FBG in a high-temperature environment. The stability of the fiber laser at high temperature was improved after the FBG was annealed at 1100 °C. The fiber laser can work stably as a temperature sensor at 1000 °C and its temperature sensing sensitivity is approximately 15.9 pm/°C from 300 °C to 1000 °C.

Phase-pure eulytite-type Sr3Y0.88(PO4)3:0.10Yb3+,0.02Ln3+ upconversion (UC) phosphors (Ln = Ho, Er, Tm) were synthesized via gel-combustion and subsequent calcination at 1250°C. Their UC luminescence, temperature-dependent fluorescence intensity ratio of thermally and/or non-thermally coupled energy levels, and performance of optical temperature sensing were systematically investigated. The phosphors typically exhibit green, orange-red and blue luminescence under 978 nm NIR laser excitation for Ln = Er, Ho and Tm, respectively, which were discussed from two- and three-photon processes. The 524 nm green (Er3+), 657 nm red (Ho3+) and 476 nm blue (Tm3+) main emissions were analyzed to have average decay times of ~52 ± 2, 260.6 ± 0.7 and 117 ± 1 μs, respectively. It was shown that (1) the Er3+ doped phosphor has a better overall performance of temperature sensing with thermally coupled 2H11/2 and 4S3/2 energy levels, whose maximum absolute (SA) and relative (SR) sensitivities are ~5.07 × 10−3 K−1 at 523 K and ~1.16% at 298 K, respectively; (2) the Ho3+ doped phosphor shows maximum SA and SR values of ~0.019 K−1 (298–573 K) and 0.42% at 573 K for the non-thermally coupled energy pairs of 5F5/(5F4,5S2) and 5I4/5F5, respectively; (3) the Tm3+ doped phosphor has a maximum SA of ~12.74 × 10−3 K−1 at 573 K for the non-thermally coupled 3F2,3/1G4 energy levels and a maximum SR of ~1.74% K−1 at 298 K for the thermally coupled 3F2,3/3H4 levels. Advantages of the current phosphors in optical temperature sensing were also revealed by comparing with other typical UC phosphors.

Developing an alternative solution to reduce or not use the rare-earth ions is of much importance. Tunable up-conversion (UC) multicolor luminescence is realized by utilizing the green UC emission of the intrinsic defects and optimizing the doping contents of Yb3+ and Tm3+ ions in the Na0.5Bi0.5-x-yYbxTmyTiO3 (NBT:xYb/yTm) ceramics. The UC white-light emission, which is close to the standard achromatic point, is achieved by an optimal design. And the possible up-conversion emission mechanism of defects and Tm3+/Yb3+ ions is also discussed. In addition, the optical temperature sensing properties were also investigated basing on the UC emission of defects in a temperature range from 83 to 683 K. The results indicate that the NBT:xYb/yTm is promising for the application as optical thermometry materials.

Tellurite glasses of TeO2 BaF2−REF3 (RE = La, Gd, and Y) co-doped with Er3+/Yb3+ were prepared and investigated comparatively for optical fiber temperature sensors. For this purpose, their thermal and optical properties were examined in detail. The J-O theory was adopted to estimate the transition properties based on absorption spectra. The dominant green emissions were observed in both of the downshifting and upconversion luminescence. The optical temperature sensing abilities based on the FIR of Er3+ green emissions were studied under both of the UV (380 nm) and NIR (980 nm) excitations. Results show that these three tellurite glasses, especially for the TBG glass, should be very qualified for the design of optical fiber temperature sensors under different excitation modes.

Though the strain characteristics of fiber Bragg gratings (FBGs) inscribed in perfluorinated graded-index (PFGI) polymer optical fibers (POFs) have been reported, their temperature characteristics have not yet been detailed. In this paper, we experimentally investigate the temperature dependence of the Bragg wavelength of a PFGI-POF-FBG. With the increasing temperature, each peak of the FBG-reflected spectrum shifted to longer wavelength with different coefficients. The temperature coefficient of one of the clearest peaks was 0.09 nm/°C, which was eight times larger than those of FBGs in silica single-mode fibers and almost the same as those of FBGs in polymethyl methacrylate POFs. A temperature-independent but strain-dependent peak was also observed, which indicates the potential of discriminative sensing of strain and temperature.

In this paper, waveguide specklegram sensor (WSS) in Nd:YAG crystal for temperature sensing based on the average intensity variation of speckle patterns has been demonstrated. The temperature sensing resolution of the WSS has been identified as high as 0.05 °C. WSS in diverse-guiding geometries with different dynamic range for the temperature sensing has been obtained. In addition, the WSS own a much more sensitive performance to temperature variation when the laser with shorter wavelength and higher power is utilized. Benefit from the compact structure, WSS can be integrated in to a lab-on-chip system offering real-time monitoring of temperature.

In the Swiss concept for the disposal of spent fuel and vitrified high-level radioactive waste, the buffer material of the engineered barrier system in the disposal tunnels consists of granulated bentonite mixtures (GBM) and blocks of highly compacted bentonite. For the GBM to perform sufficiently as a barrier, the dry density of the emplaced GBM is an essential parameter as well as a quality control indicator at the time of tunnel backfilling. In this study, an actively heated fiber-optic cable combined with distributed temperature sensing was applied with the aim of estimating the in-situ dry density distribution of the GBM. A set of experiments was performed using GBM specimens with controlled dry density conditions at the Grimsel Test Site in Switzerland to examine how the thermal responses vary with the dry density of the GBM material. The results indicated that the thermal responses were sufficiently sensitive to allow distributed temperature sensing in combination with an actively heated fiber-optic cable to be used as a reliable tool for estimating the dry density profile in the tunnels backfilled and sealed with the GBM along the cable with a high resolution.

LnNbO4:Er3+ (Ln = Lu, Y, Gd) phosphors were prepared through a conventional solid-state reaction method. The phase purity of the samples was characterized by X-ray diffraction (XRD). A comparative study of spectral and temperature sensing properties of LnNbO4:Er3+ (Ln = Lu, Y, Gd) phosphors was presented. The excitation spectra of the samples show a strong band in the region of 200–350 nm coming from the NbO44−, thus indicating efficient energy transfer from the host to Er3+. From the dependence of upconversion (UC) luminescence spectra on laser diode working current, it was confirmed that 2- and 3-photon processes were respectively responsible for both the green and the red UC emissions under 980 and 1550 nm excitations. The temperature sensing properties for LnNbO4:Er3+ were compared under individual excitation of 980 and 1550 nm. It was found that the temperature sensing was independent from the excitation wavelength, but LuNbO4:Er3+ phosphors yielded the highest luminescence intensity and maximum temperature sensitivity.

We theoretically investigate the temperature-dependent Goos-Hanchen (GH) shifts in a symmetrical graphene-cladding waveguide (SGCW). The GH shifts in SGCW present a quasi-periodic tendency near the resonance angle with the change of temperature, which can mainly be attributed to the temperature dependence of the guiding layer’s thickness, instead of the graphene intraband conductivity and guiding layer’s refractive index. Importantly, tiny temperature fluctuations can cause significant deviations in GH shifts, and the deviations can be efficiently improved by adjusting the Fermi energy. Therefore, we propose a high-sensitivity temperature sensing scheme based on GH shifts in the SGCW, and the maximum sensitivity can reach up to −2.2 × 105 μ m/ ° C. These researches may open avenues for applications of optical temperature sensors.

A stable single wavelength random fiber laser (RFL) with a partial-reflection random fiber grating (PR-RFG) for high temperature sensing is proposed and demonstrated for the first time, to the best of our knowledge. The PR-RFG is fabricated with the help of a femtosecond laser, with its highest reflection peak significantly higher than all other reflection peaks, which can ensure the stability of this filter-free RFL. Theoretical calculations also show that such a PR-RFG should be designed with reflectivity in the range of ∼ 30 % − 90 % to obtain one reflection peak significantly higher than other peaks. The threshold of this laser is only 6.4 mW. In addition, the RFL realizes temperature sensing in the range from 25°C to 500°C and has an optical signal-to-noise ratio of up to 70 dB.

We congratulate Kar et al. on their elegant study evaluating ex-vivo temperature profiles and the resulting thermal injury formation on the epiesophageal surface during radiofrequency (RF) ablation. In addition to being the first study to detail temperature profiles inclusive of the epiesophageal surface during RF ablation, we believe that the results add further concern to the use of temperature sensing technology in the quest to reduce esophageal injury. Three recent clinical trials have evaluated the efficacy of luminal esophageal temperature (LET) monitoring and found either no benefits, or signals of harm. On the other hand, two pilot RCTs suggest benefits of active cooling, and a large RCT, the IMPACT study, further confirms this benefit by finding an 83% reduction in esophageal lesion formation using an active cooling device. With no degradation in ablation efficacy, as well as a reduction/elimination of the need for fluoroscopy and reports of shortened procedure time with active cooling technology, the data of Kar et al., combined with growing clinical data, suggest that continued use of LET monitoring may be unjustified.

A novel tunable Erbium-doped fiber ring laser (EDFRL) with a cascaded-chirped long-period fiber grating (C-CLPG) as a wavelength selection filter is proposed from the viewpoint of the sensor use, in which a variable optical attenuator (VOA) is employed as an intracavity loss modulator to change the oscillation wavelength region so that the resultant tuning wavelength range is widened. In the demonstrative experiment for temperature measurements, oscillation over the wavelength range of 12.85 nm (1557.62~1570.47 nm), which is more than three times range of the previously presented laser and is equivalent to 64 °C in terms of temperature change, was achieved, while a single-wavelength oscillation was maintained. In addition, a practical technique for realizing a temperature measurement by combining with the VOA control is also discussed.

The optical fiber temperature and refractive index sensor combined with the hollow needle structure for medical treatment can promote the standardization of traditional acupuncture techniques and improve the accuracy of body fluid analysis. A double-parameter sensor based on fiber Bragg grating (FBG) is developed in this paper. The sensor materials are selected through X-ray diffraction (XRD) analysis, and the sensor sensing principle is theoretically analyzed and simulated. Through femtosecond laser writing pure silica fiber, a high temperature resistant wavelength type FBG temperature sensor is obtained, and the FBG is corroded by hydrofluoric acid (HF) to realize a high-sensitivity intensity-type refractive index sensor. Because the light has dual characteristics of energy and wavelength, the sensor can realize simultaneous dual-parameter sensing. The light from the lead-in optical fiber is transmitted to the sensor and affected by temperature and refractive-index, then, the reflection peak is reflected back to the lead-out fiber by the FBG. The high temperature response and the refractive index response of the sensor were measured in the laboratory, and the high temperature characteristics of the sensor were verified in the accredited institute. It is demonstrated that the proposed sensor can achieve temperature sensing up to 1150 °C with the sensitivity of 0.0134 nm/°C, and refractive sensing over a refractive range of 1.333 to 1.4027 with the sensitivity of −49.044 dBm/RIU. The sensor features the advantages of two-parameter measurement, compact structure, and wide temperature range, and it exhibits great potential in acupuncture treatment.

Distributed Fibre optic Sensing is an innovative technology enabling to turn a fibre optic cable into hundreds to thousands of sensors. This solution can be adapted for temperature, strain or acoustic sensing using a same optical fibre. It then appears as a powerful leverage for the monitoring of Enhanced Geothermal Systems during geothermal production. In the framework of the European funded project MEET, FEBUS OPTICS has been mandated for deployment and exploitation of a fibre optic cable in an observation well located in the geothermal plant of Soultz-sous-Forêts. Distributed Temperature Sensing, Distributed Strain and Temperature Sensing and Distributed Acoustic Sensing monitoring have been achieved at various moments after the fibre optic cable descent. We observe and discuss here the results of those acquisition campaigns.

Distributed temperature sensing with 10 dB back-reflection-enhanced fiber is performed based on φ-OTDR. While the temperature sensitivity of such fibers is similar to that of standard single-mode fibers, a 3-times higher temperature resolution is observed.

The authors wish to make the following two corrections to this paper [...]

We describe a new approach in Raman temperature sensing based on broadband incident light. The reported results show the proof of concept and thus form an important basis for future distributed temperature sensing systems.

Femtosecond laser direct writing was used to continuously induce Rayleigh scattering centers in meters of single-mode optical fiber using a customized roll-to-roll setup, which can be used to improve the performance of scattering-based distributed sensing.

The first observation of resurgence of regenerated fiber Bragg gratings in six-hole microstructured optical fibers useful for temperature sensing beyond 1400 °C is investigated. These R2FBGs can withstand extreme temperatures of up to 1452 °C.

Temperature sensing is essential for the survival of living organisms. Some reptile embryos can reposition themselves within the egg to seek optimal temperatures, but the molecular sensors involved in this temperature detection remain unknown. Here, we show that such thermotaxic behavior is directly determined by the activation of two heat-sensitive ion channels of the turtle: the transient receptor potential ankyrin 1 (MrTRPA1) and transient receptor potential vanilloid-1 (MrTRPV1). These two TRP channels were found to exhibit distinctive distributions among turtle dorsal root ganglion (DRG) neurons. Additionally, our laser irradiation assays illustrated that the heat activation thresholds of MrTRPA1 and MrTRPV1 are consistent with the mild (28-33°C) and noxious (>33°C) heat determined by behavioral tests, respectively. Further pharmacological studies have demonstrated that ligand-induced intervention of MrTRPA1 or MrTRPV1 is sufficient to mimic heat stimuli or block temperature signaling, causing changes in embryo movement. These findings indicate that the initiation of thermotaxic response in turtle embryos relies on a delicate functional balance between the heat activation of MrTRPA1 and MrTRPV1. Our study reveals, for the first time, a unique molecular mechanism underlying thermal detection: the two TRP channels act as a physiological tandem to control the thermotaxic behavior of turtle embryos.

The design and construction of a waste rock pile influences water infiltration and may promote the production of contaminated mine drainage. The objective of this project is to evaluate the use of an active fiber optic distributed temperature sensing (aFO-DTS) protocol to measure infiltration and soil moisture within a flow control layer capping an experimental waste rock pile. Five hundred meters of fiber optic cable were installed in a waste rock pile that is 70 m long, 10 m wide, and was covered with 0.60 m of fine compacted sand and 0.25 m of non-reactive crushed waste rock. Volumetric water content was assessed by heating the fiber optic cable with 15-min heat pulses at 15 W/m every 30 min. To test the aFO-DTS system 14 mm of recharge was applied to the top surface of the waste rock pile over 4 h, simulating a major rain event. The average volumetric water content in the FCL increased from 0.10 to 0.24 over the duration of the test. The volumetric water content measured with aFO-DTS in the FCL and waste rock was within ±0.06 and ±0.03, respectively, compared with values measured using 96 dielectric soil moisture probes over the same time period. Additional results illustrate how water can be confined within the FCL and monitored through an aFO-DTS protocol serving as a practical means to measure soil moisture at an industrial capacity.

This study aims to validate and track valve positions for all the zones applying recorded distributed temperature sensing (DTS) data interpretation to propose the best combination of downhole inflow control valve (ICV) openings to optimize Well X-2 multizone commingled production. Fiber DTS is relied on as an innovation against downhole conditions that has compromised the three out of four downhole dual-gauges and valve position sensors. For zonal water control purpose, ICV cycling and positioning have been attempted in 2019. The valve position tracking derived from the compromised downhole dual gauges and valve position sensors does not tally with the surface flow indication overall. Consequently, the original measurement intention of the fiber DTS as back-up zonal-rate calculation profiling and as potential sub-layer flow-contribution indicators is brought in as contingency zonal valve-opening tracking and guide that proved valuable for subsequent production optimization. Downloaded DTS data is depth matched and validated against known operating conditions like time of each cycling stage and surface well test parameters (i.e. Liquid Rate, Watercut, Tubing Head Pressure (THP), Total Gas, Gas-Oil Ratio (GOR)), etc. To establish a baseline, several DTS traces of historical operating condition during a known stable period were selected, i.e. stable flowing condition at only Zone 4stable shut-in condition at surface with only ICV Zone 4 is opened Downhole valve-position tracking can be interpreted alternatively from induced fiber temperature activities across the valve depth with a good temperature baseline benchmarking from DTS temperature profiling. In one of these alternative interpretations based on fiber temperature, it is found and validated that Zone 1 ICV is Closed, Zone 2, 3 and 4 are in opened position and continuously producing at any cycles. This is in conflict of zonal production control understanding initially based on the compromised downhole sensor indicating that all the zonal valves are supposedly in fully closed position. In this case-study, DTS data has been proven useful and as an innovative alternative to determine downhole valve opening with analogue to flow contribution derivation methodology. Therefore, anytime in the future where Well X-2 valves cycling is planned to be carried out, there is a corresponding operating procedure that needs to incorporate onsite real-time DTS data monitoring to validate tracked valves positioning.

This paper presents a unique compact passive UHF RFID tag that is capable of hosting a temperature sensor for wireless sub-soil measurements. In particular, a newly developed dipole antenna is matched to the complex conjugate of the temperature sensing passive RFID AMS SL900A IC at 900 MHz. A prototype tag is then buried 7.62 cm in the top soil of a field used for agricultural purposes and the read range is measured. It is shown that the sensor has a maximum measured read range of 0.5 m in the field and has a 50% reduction in overall size when compared to previously reported designs. Moreover, it was demonstrated that the prototype can transmit accurate temperature data of the soil. These measurements of the tag in the field demonstrate that the proposed low-profile UHF RFID tag can be used in other sub-soil applications to support precision agriculture.