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A temperature sensor based upon a single mode - multimode-single mode – multimode - single mode (SMSMS) fiber structure is experimentally demonstrated. The SMSMS structure is covered by ethanol-glycerol solution, and changing the ratio of ethanol to glycerol changes the temperature sensitivity. A theoretical calculation was developed to characterize the influence of the ethanol-glycerol content upon the sensor performance,. Multimode interference (MMI) occurs between single mode fibers (SMF) and multimode fibers (MMF), and temperature measurements were achieved by monitoring the movement of the interference profile in the transmission spectrum. The results show that covering the SMSMS structure with an ethanol-glycerol solution improves the temperature sensitivity of the sensor. The temperature sensitivity was is 0.700 nm/°C from 30 °C to 80 °C. [ABSTRACT FROM AUTHOR]

We propose a dual-channel surface plasmon resonance (SPR) sensor based on hollow-core fiber (HCF) for the simultaneous measurement of the liquid refractive index (RI) and ambient temperature. The simultaneous monitoring of two parameters can effectively realize the temperature compensation of liquid RI measurement. One channel is coated with a silver film to sense the liquid RI, the other channel is coated with a gold film and polydimethylsiloxane (PDMS) to sense the ambient temperature, and the cross sensitivity of the multi-parameter measurement is solved using the dual-wavelength matrix method. The sensing performance of the proposed sensor is investigated both theoretically and experimentally, which proves that it can achieve high sensitivity in a relatively wide measurement range. The experiment shows that the liquid RI sensitivity is as high as 2400.079 nm/RIU in the RI range of 1.3333–1.3770, and the temperature sensitivity is −1.29 nm/°C in the temperature range of 40 °C–90 °C. This work provides a new scheme for the multi-parameter measurement, and the proposed sensor has the advantages of simple and compact structure, low cost, wide measurement range and high sensitivity, which promises broad application prospects in the simultaneous monitoring of liquid RI and temperature. [ABSTRACT FROM AUTHOR]

In this work, a new method was explored for developing temperature and relative humidity (RH) optical fiber sensors based on surface plasmon resonance (SPR). A SPR optical fiber sensor coated with carboxymethyl cellulose (CMC) and polydimethylsiloxane (PDMS) was proposed for the simultaneous measurement of RH and temperature. The sensor was fabricated by connecting two no-core optical fibers (NCFs) using multimode optical fibers (MMFs). Metal films were deposited on the surface of NCFs and further coated with CMC and PDMS. CMC coating was used for RH sensing based on the change of refractive index (RI) caused by water absorption; PDMS coating was used for temperature sensing based on its RI change with temperature. Univariate analysis showed that there was very weak interaction between RH and temperature measurement. For RH sensing, the sensitivities were −1.230 nm/RH%, −2.932 nm/RH% and −0.431 nm/RH% when RH were 50%~65%, 65%~70% and 70%~80%, respectively; for temperature sensing, the sensitivity was −2.213 nm/°C at 10 °C~50 °C. The proposed sensor can not only respond to both temperature and RH variation, but also compensate the cross sensitivity between the two parameters. It is simple in structure, easy to manufacture and efficient in the simultaneous detection of temperature and RH, which promises great application prospects in the fields of agriculture, food industry, biological field and other production activities. [ABSTRACT FROM AUTHOR]

A Fabry-Perot interferometer (FPI) temperature sensor was proposed by splicing a self-made hollow core anti-resonance fiber (HC-ARF) between two single mode fibers (SMFs). The HC-ARF was 2 mm long and one SMF was 20 mm in length. The SMF end face was coated with an Au film. When temperature varied from 45 °C to 85 °C, a sensitivity of 81.1 pm/°C was obtained at the waveband of 1550 nm∼1555 nm. When temperature varied from 35 °C to 95 °C, a sensitivity of 138.8 pm/°C was obtained at the waveband of 1571 nm∼1581 nm. Theoretical analysis suggested that the sensitivity of this proposed sensor can be easily adjusted by varying the length of the Au-coated SMF via the Vernier effect, which was confirmed by a subsequent experiment where the SMF length was varied from 20 mm to 170 mm. This work offers a simple sensitivity control method, and the proposed sensor is easy to manufacture, compact in structure, and convenient in performance control, which can be applied for a wide range of biological and chemical applications. [ABSTRACT FROM AUTHOR]

This article presented an investigation of nonlinear temperature sensing based on soliton self-frequency shift (SSFS) in an in-house fabricated microstructured optical fiber (MOF), and the sensing performance was evaluated by detecting the peak wavelength shift of soliton with the variation of temperature. Both theoretical simulation and experimental research were carried out and there was a good correspondence between the two results. The experimental sensitivity was as high as 0.451 nm/°C at 400 mW with a resolution of 0.2653 °C. Our work is a proof of concept of the optical fiber nonlinear phenomenon of SSFS to sensing technology. This temperature sensor does not involve additional fiber modification, and it has potential applications in biomedical, security, and harsh industrial environment. [ABSTRACT FROM AUTHOR]

Multi parameter measurement and device miniaturization are the development trend of optical fiber sensors. Here we propose a compact dual channel surface plasmon resonance (SPR) fiber sensor which can measure the liquid refractive index (RI) and ambient temperature in real time. This sensor coats metal and polydimethylsiloxane (PDMS) on the side of a no-core D-shaped fiber: the channel for measuring the liquid RI is covered by silver film, and the channel for temperature sensing is covered by gold film and PDMS. The sensing sensitivity is analyzed by finite element method. When the liquid RI is within 1.33~1.44 and the temperature is within 0~180 °C, the corresponding maximum spectral sensitivity is 12530 nm/RIU and −3.465 nm/°C, respectively. The sensor has wide detection range, compact structure and temperature compensation function, which is suitable for environmental monitoring and high-precision sensing. [ABSTRACT FROM AUTHOR]

Due to the unique optical properties and good thermal stability, GeAsSeTe microstructured optical fiber (MOF) offers tremendous opportunity for applications in mid-infrared range (MIR). In this article, we design a CS2-filled GeAsSeTe MOF whose core, inner and outer cladding adopt Ge15As25Se15Te45, Ge20As20Se17Te43 and Ge20As20Se15Te45 glass, respectively. Highly efficient four-wave mixing (FWM) is realized and ultrabroadband optical parametric gain is obtained. By analyzing the central parametric gain bandwidth change with the temperature variation, this CS2-filled GeAsSeTe MOF is proved to be highly sensitive concerning temperature sensing, the sensitivity being as high as 2.32nm/°C from −80°C to 45°C. Such high temperature sensing property have key prominence for developing optical fiber temperature sensor in MIR region based on FWM. To the best of our knowledge, this is the first study to propose temperature sensing in the MIR by drawing on central parametric gain bandwidth of FWM change in a GeAsSeTe MOF. [ABSTRACT FROM AUTHOR]

A biocompatible and robust fiber surface plasmon resonance (SPR) temperature sensor was fabricated based on an alcohol-filled hollow-core fiber. The fabrication process of this designed sensor included Ag film coating, liquid injection, and fusion splicing, which was low cost and efficient. Due to the high refractive index sensitivity of the SPR effect and the high thermal optical coefficient of alcohol, the designed sensor performed well in temperature sensing, whose linear sensitivity reached as high as 1.16 nm/°C in the range of 35.5 °C–70.1 °C. Being small in size, low in fabrication cost, and highly sensitive in performance, this sensor is suitable for temperature detection during biological and chemical reactions and has the potential to realizing multiparameter or distributed temperature measurement. [ABSTRACT FROM AUTHOR]

A novel curvature sensor was proposed based on a dual-core photonic crystal fiber (PCF) that was spliced between two single-mode fibers (SMFs). The sensor sensitivity was investigated both analytically and experimentally, and the influence of the PCF length and temperature on the sensor performance was also analyzed. The results showed the sensor had different sensitivity with different bending direction and its highest sensitivity can reach 10.14 nm/m−1. It also showed great insensitivity to temperature interference. Being of simple structure and good mechanical strength, this curvature sensor has great application potential in various fields, such as architecture, machinery, robot, wearable sensor, and so on. [ABSTRACT FROM AUTHOR]

A D-shaped photonic crystal fibre filled with liquid crystal was demonstrated as an amphibious sensor for detection of both temperature and refractive index, when combined with plasma materials. Specifically, the optical component is implanted into a complete optical system ensuring modulation of the external electric field. When the refractive index of the external solution changes from 1.0 to 1.6, the y-polarised mode has a loss spectrum with a wavelength sensitivity of up to 2275 nm/RIU, and the corresponding amplitude sensitivity is −88.2RIU−1. When the perceived temperature changes from 15°C to 50°C, the temperature of the sensor is correspondingly expressed as the maximum wavelength sensitivity of 9.09 nm/°C and the amplitude sensitivity of −0.311°C−1. In addition, the actual micro-operation processes have been studied in detail, such as polishing depth, coating thickness and coating method. This provides practical ideas for real-time sensing analysis that requires harsh environments. [ABSTRACT FROM AUTHOR]

In this study, the silver mirror reaction was used to coat the silver film on the surface of self-made microstructured fiber (MSF) to stimulate the surface plasmon resonance effect, and Polydimethylsiloxane (PDMS) with a high thermal-optical coefficient was coated on the silver film as temperature-sensitive material. The MSF with silver and PDMS films was coupled with multi-mode fiber on both sides to form the temperature sensor. In this sensor system, the energy is coupled into the cladding of the microstructure fiber by multi-mode fiber, and the surface plasmon resonance can be further excitated in the MSF. When the temperature of the external environment changes, the refractive index of PDMS will also change. At this time, combined with the surface plasmon resonance effect, a resonant absorption peak corresponding to the temperature appears in the transmission spectrum so that the temperature can be measured quickly and accurately. We found that, in the temperature range of 35 °C to 95 °C, the average temperature sensitivity of the sensor during heating and cooling was −0.83 nm/°C and −0.84 nm/°C, respectively. The advantages of this sensor are the simple structure, convenient operation and good reversibility. The relative sensitivity deviation value (RSD = 0.0059) showed that the sensor has high stability. The temperature sensor based on MSF has favorable prospects for use in fields such as medical treatment, biochemical detection and intelligent monitoring. [ABSTRACT FROM AUTHOR]

In this work, a surface plasmon resonance (SPR) temperature sensor based on a con-joined-tubular anti-resonance optical fiber (CTF) was theoretically designed and analyzed using the finite element method. The CTF cladding was composed of eight pairs of conjoined tubes, and one or two holes of the tubes were selectively coated with gold to generate the SPR effect. Alcohol was injected into the core of the CTF to work as the sensing medium using vapor deposition. The proposed sensing structure exhibited excellent birefringence and produced more than six resonant peaks in different wavebands of the X and Y polarization. The positions of those resonant peaks were sensitive to temperature change, and the simulated sensitivity was about 3.2–3.6 nm/°C. The multiple working wavebands of the proposed sensing structure could be used for self-verification. Moreover, the influence of structural parameters on sensing performance was analyzed in detail. Possessing features of high sensitivity, good birefringence, multiple measuring wavebands, and self-verification, the proposed CTF-based SPR sensor has great potential in practical applications such as biological research and chemical sensing. [ABSTRACT FROM AUTHOR]

For this study, a temperature sensor utilizing a novel tellurite photonic crystal fiber (PCF) is designed. In order to improve the sensor sensitivity, alcohol is filled in the air holes of the tellurite PCF. Based on the degenerate four-wave mixing theory, temperature sensing in the mid-infrared region (MIR) can be achieved by detecting the wavelength shift of signal waves and idler waves during variations in temperature. Simulation results show that at a pump wavelength of 3550 nm, the temperature sensitivity of this proposed sensor can be as high as 0.70 nm/°C. To the best of our knowledge, this is the first study to propose temperature sensing in the MIR by drawing on four-wave mixing (FWM) in a non-silica PCF. [ABSTRACT FROM AUTHOR]

In this paper, a temperature sensor based on fluorescence intensity ratio (FIR) technique is prepared by the dual curing method. The pumping threshold is only 0.1 mW for the application of real-time thermal monitoring on small transformers. This not only greatly reduces the thermal effects accumulated by laser irradiation but also contributes to the integration and portability of the light source. Based on the FIR, the temperature information could be demodulated through tracking the fluorescence spectral changes. The basic temperature sensing characteristics of this sensor were evaluated, which showed that the maximum stability deviation and reproducibility error were within ±1.1 K and ±0.8 K, respectively. Notably, it has a maximum measurement error of only 0.61 K when applied to the temperature monitoring of transformers. And a fast time response of 2.1 s was exhibited in the cyclic exhalation experiment. This proposed sensor is suitable for mass production due to its resistance to electromagnetic interference, low pumping power, fast time response, excellent stability and reproducibility. [ABSTRACT FROM AUTHOR]

In this study, the green up-conversion (UC) fluorescence emission in Er3+/Yb3+/Mo6+ tri-doped tellurite glasses (TeO 2 –ZnO–Li 2 CO 3 –Bi 2 O 3 , TZLB) was explored for temperature sensing. The doping of Mo6+ ions allowed enhanced luminescence at moderate power pumping, avoiding the introduction of undesired laser-induced thermal effects while improving the spectral signal-to-noise ratio. The luminescence characteristics were investigated in detail at different doping molar ratio of Mo6+ ions, and the strongest was observed at 8 mol%. Drawing on tri-doped TZLB glass with the strongest UC emission intensity, a tri-doped TZLB fiber was fabricated and coupled with two multimode fibers (MMFs) via Ultraviolet (UV) adhesive, forming the temperature sensor. The sensor was further encapsulated by a silica tube sealed with Ultraviolet adhesive, overcoming the poor mechanical property of tellurite fiber. The temperature information could be demodulated based on the fluorescence intensity ratio technique. The temperature sensing performance of the tri-doped TZLB sensor was investigated as temperature varied from 258 to 420 K and its repeatability was experimentally verified. The Er3+/Yb3+/Mo6+ tri-doped TZLB has an application prospect in the field of lighting, and the so-based temperature sensor is expected to be applied to thermal detection in the fields of medical diagnostics, environmental monitoring, and optical thermometers, etc. [ABSTRACT FROM AUTHOR]

• An innovative structure design and sensing theory combination were proposed. • High sensitivity temperature sensor was achieved by PDMS microcavity. • Simple basic SMSMS structure lowered the fabrication difficulty. • Combined SMSMS + PDMS cavity structure brought sensing improvement for about 7 times. • Two combined sensors can cross-correct within the intersected detection range. • With simple manufacture steps, higher temperature sensitivity and bigger sensing range are achieved. In this paper, an optic-fiber temperature sensor is proposed with an innovative structure design and sensing theory combination. The structure design is consisted of classic SMSMS structure and a polydimethylsiloxane (PDMS) microcavity, which is formed by inserting single mode fibers (SMF) and multimode fibers (MMF) from both ends of a hollow core fiber (HCF) filled with uncured PDMS. By adjusting the length (L) of the cavity into proper value, the reflection temperature sensitivity reaches up to −567.86 pm/℃, and the transmission sensitivity reaches −120.69 pm/℃. Due to the presence of the PDMS microcavity, the reflection spectrum achieved highly sensitive temperature Fabry-Perot interferometer (FPI) sensor. Moreover, a Mach-Zehnder interferometer (MZI) temperature sensor also formed by monitoring the transmission spectrum, and its temperature sensitivity is elevated about 7 and 1.2 times compared with the pure splicing SMSMS and the splicing + PDMS coating structure. By deploying the PDMS microcavity, FPI sensor and MZI sensor were combined inside one device with significant temperature sensing performance, and these two combined sensors can cross-correct within the intersected detection range. With simple manufacture steps, higher temperature sensitivity and bigger sensing range are achieved. [ABSTRACT FROM AUTHOR]

Utilizing a hybrid waveguide comprising microfiber and graphene oxide (GO), this study introduced an innovative temperature sensor based on four-wave mixing (FWM) effect. The methodology involved a tunable continuous wave (TCW) laser and a self-engineered all-fiber mode-locked laser operating at 1560 nm. The microfiber, featuring a minimum diameter of 10 μm, was fabricated through the flame fusion tapering technique, and the microfiber surface was coated with a GO film through the spontaneous evaporation of a GO solution. To improve the stability and robustness of the sensor, a layer of polydimethylsiloxane (PDMS) was applied to the surface as a protective coating. The GO film compensated for dispersion in conjunction with microfiber, enhanced nonlinearity and facilitated low-power FWM phenomena. Furthermore, it increased temperature sensing sensitivity. By measuring the center wavelength shift of the idler and signal light, we achieved a temperature sensing sensitivity of −2.08 nm/℃ from −15 ℃ to 20 ℃ using the CW laser at 1540 nm. This sensor also had a resolution of 0.024 ℃, a response time of 0.12 s and a maximum temporal resolution of 0.08 s. Our study marks the initial investigation of a temperature sensing mechanism employing the FWM phenomenon within this unique hybrid waveguide. It serves as a proof of concept for using a microfiber combined with the two-dimensional material GO film to generate nonlinear FWM for temperature sensing. Continuous optimization of experimental conditions and waveguide dimensions is expected to enhance sensing performance. This opens up new avenues for future research in novel optical sensing technology, particularly in the exploration of high-performance sensors through the integration of nonlinear phenomena with different two-dimensional materials, showcasing substantial research potential. [Display omitted] • This study explores microfiber and graphene oxide film (GO) for nonlinear four-wave mixing (FWM) temperature sensing, suggesting future research in combining nonlinear phenomena with 2D materials for high-performance sensors. • GO film boosts sensor sensitivity and nonlinearity, compensates dispersion with microfiber, shifts to anomalous dispersion at 1550 nm, and lowers the FWM power threshold. • Temperature sensitivity within the range of −15 °C to 20 °C is −2.08 nm/°C, with a resolution of 0.024 °C, a response time of 0.12 s and a maximum temporal resolution of 0.08 s. • The conversion efficiency of four-wave mixing can reach −19.5 dB. [ABSTRACT FROM AUTHOR]

In this paper, a surface plasmon resonance refractive index and temperature sensor based on V-cut photonic crystal fiber (PCF) is proposed. The proposed structure is studied and analyzed using the finite element method (FEM). The sensing area is a V-shaped cut groove, and the cases when the cut angle is positive, 0° and negative are discussed and compared. The results show that when the cutting angle is 15°, the optimal sensing performance can be obtained compared with other cutting angle. By optimizing other structural parameters when the cutting angle is 15°, in the refractive index range of 1.34–1.38, the average sensitivity of the refractive index sensor is 10,500 nm/RIU, and the maximum sensitivity is 52,500 nm/RIU. The average sensitivity is 5.57 nm/°C in the range of 85 ℃–145 ℃ as a temperature sensor. Due to the simple structure and high sensitivity of the design, it can be used for real-time monitoring of analytes in medical, biochemical and environmental monitoring. [ABSTRACT FROM AUTHOR]

• A nonlinear temperature sensor was proposed drawing on soliton self-frequency shift (SSFS). • This work applied nonlinear technology to the field of sensing. • This work overcomes the complex structure and low mechanical strength of traditional optical fiber sensors. [Display omitted] A novel fiber-optic soliton self-frequency shift (SSFS) temperature sensor fabricated using an in-house-made microstructured optical fiber was proposed. Based on this sensor, SSFS-based sensing was systematically investigated with the variation of average pump power and pump wavelength. By detecting the central wavelength shift of the 3-dB bandwidth of the soliton with the change in temperature, the sensing performance of the proposed sensor was evaluated experimentally and theoretically, subject to the average pump power and pump wavelength. At the generation of the fundamental soliton, when the pump wavelength was fixed, the higher the average pump power, the higher the temperature sensitivity. When the average pump power was fixed, the longer the pump wavelength, the higher the temperature sensitivity. The maximum temperature sensitivity of the proposed sensor was 1.759 nm/℃ at an average pump power of 300 mW and pump wavelength of 1600 nm. This temperature sensor exhibited excellent properties, such as high sensitivity, a simple structure, an easy fabrication process, good mechanical strength, and low cost, rendering it highly applicable in fields such as food quality control, environmental monitoring, and biomedical testing. [ABSTRACT FROM AUTHOR]