Highly sensitive optical fiber temperature sensor based on resonance in sidewall of liquid-filled silica capillary tube

A highly sensitive optical fiber temperature sensor based on a section of liquid-filled silica capillary tube(SCT)between single mode fibers is proposed. Two micro-holes are drilled on two sides of SCT directly by using femtosecond laser micromachining, and liquid polymer is filled into the SCT through the micro-holes without any air bubbles and then sealed by using ultra-violet(UV) cure adhesive. The sidewall of the SCT forms a Fabry–Perot resonator, and loss peaks are achieved in the transmission spectrum of the SCT at the resonant wavelength. The resonance condition can be influenced by the refractive index variation of the liquid polymer filled in SCT, which is sensitive to temperature due to its high thermooptical coefficient(-2.98 × 10^-4℃^-1). The experimental result shows that the temperature sensitivity of the proposed fiber structure reaches 5.09 nm/℃ with a perfect linearity of 99.8%. In addition, it exhibits good repeatability and reliability in temperature sensing application.

A radiation–temperature coupling model of the optical fiber attenuation spectrum in the Ge/P co-doped fiber

A radiation–temperature coupling model of optical fiber attenuation spectrum has been developed.The spectrum in Ge/P co-doped fiber ranging from 800 nm–1600 nm at different temperatures and doses was measured and decomposed according to the configurational coordinate model based on which the power-law model was employed to predict the intensity of the color center absorption band at different doses.And the fiber loss in space was predicted by the model.This work will benefit the application of fibers in a complicated radiation environment.

Network Integration of Distributed Optical Fiber Temperature Sensor

The integration of distributed optical fiber temperature sensor with supervisory control and data acquisition （SCADA） system is proposed and implemented. In the implementation of the integration, both the compatibility with traditional system and the characteristics of distributed optical fiber temperature sensor is considered before Modbus TCP/IP protocol is chosen. The protocol is implemented with open source component Indy. The Modbus TCP/IP protocol used in the system is proved to be fast and robust.

Flexible Optical Waveguide Bent Loss Attenuation Effects Analysis and Modeling Application to an Intrinsic Optical Fiber Temperature Sensor

The temperature dependence of the bending loss light energy in multimode optical fibers is reported and analyzed. The work described in this paper aims to extend an initial previous analysis concerning planar optical waveguides, light energy loss, to circular optical waveguides. The paper also presents à novel intrinsic fiber optic sensing device base on this study allowing to measure temperatures parameters. The simulation results are validated theoretically in the case of silica/silicone optical fiber. A comparison is done between results obtained with an optical fiber and the results obtained from the previous curved optical planar waveguide study. It is showed that the bending losses and the temperature measurement range depend on the curvature radius of an optical fiber or waveguide and the kind of the optical waveguide on which the sensing process is implemented.

Temperature sensor based on a single-mode tapered optical fiber

A temperature sensor is demonstrated and fabricated by coating the single-mode tapered optical fiber with temperature-sensitive silicone rubber. It works on the change of the evanescent fields in the tapered optical fiber. Small changes in the refractive index of coating film greatly influence the power of evanescent fields, which modulate the transmission optical power in the waist region. The range of temperature measured is from -20℃ to 70 ℃. The results show that the temperature sensor has high temperature sensitivity （0.012 mW/℃） and good repeatability.

Analysis of the blackbody-radiation shift in an ytterbium optical lattice clock

We accurately evaluate the blackbody-radiation shift in a171 Yb optical lattice clock by utilizing temperature measurement and numerical simulation. In this work. three main radiation sources are considered for the blackbody-radiation shift, including the heated atomic oven, the warm vacuum chamber, and the room-temperature vacuum windows. The temperatures on the outer surface of the vacuum chamber are measured during the clock operation period by utilizing seven calibrated temperature sensors. Then we infer the temperature distribution inside the vacuum chamber by numerical simulation according to the measured temperatures. Furthermore, we simulate the temperature variation around the cold atoms while the environmental temperature is fluctuating. Finally, we obtain that the total blackbody-radiation shift is -1.289（7）Hz with an uncertainty of 1.25×10;for our;Yb optical lattice clock. The presented method is quite suitable for accurately evaluating the blackbody-radiation shift of the optical lattice clock in the case of lacking the sensors inside the vacuum chamber.

Temperature dependence of the refractive index of optical fibers

Many experimental investigations on the temperature dependence of the refractive index of optical fibers have been reported previously, however a satisfying theoretical explanation for it is still absent. In this paper, a theoretical model about the temperature dependence of the refractive index of optical fibers is presented and it is in agreement with the previous experimental results. This work is a significant reference for the research and development of temperature sensors based on optical fiber delay lines.

Novel Fiber Optic Temperature Sensor with Full Compensation Based on Optical Absorption

A novel system configuration of fiber optic sensor based on optical abso rption is proposed. Several compensation measures are discussed. A simulated exp eriment is designed and the output curve of system is given. The experiment al result shows that these compensation measures are effective on dynamic distu rbances which are caused by background light and optical fiber bend. In addition , the drifts in the light source intensity, fiber losses, and photodetector effi ciency are also compensated.

Mathematical Model of Fiber Optic Temperature Sensor Based on Optic Absorption and Experiment Testing

On the basis of analysis on the temperature monitoring methods for high voltage devices, a new type of fiber optic sensor structure with reference channel is given. And the operation principle of fiber optic sensor is analysed at large based on the absorption of semiconductor chip. The mathematical model of both devices and the whole system are also given. It is proved by the experiment that this mathematical model is reliable.

The Influences of Inorganic Scintillator Optical Fiber Radiation Dosimeter in Some Conditions

In order to meet the increasing demands of modern radiotherapy, real time in-vivo dose measurement has recently attracted significant attention. A small, flexible optical fiber radiation dosimeter, with high signal-to-noise ratio (SNR) that employs inorganic scintillator materials is presented. In this paper, some properties are investigated under special conditions, such as saturation properties when the intensity of the X-Ray is increased and the influence of the temperature of the environment. These properties are important to practical considerations if the sensor is to be successfully deployed in-vivo.

Measurement of Gamma-Rays Induced Luminescence Generated in a Sapphire Based Fiber-Optic Radiation Sensor

In this study, we fabricated a sapphire based fiber-optic radiation sensor. To evaluate the fiber- optic radiation sensor, we measured the spectrum and intensity of the luminescence generated from the fiber-optic radiation sensor according to the thickness of the PMMA block by irradiation of gamma rays emitted from a Co-60 source. And the result was compared with the value calculated from the formula of Lambert-Beer.

All-Fiber Optic Temperature Sensor

This paper presents a new class of all fiber optic temperature sensor, of which the heat expansion thin film is coated on the etched fiber. The sensitivity of the sensor is increased and the shape size is decreased. This sensor possesses the linear temperature response and the good repeatability. These sensors can be used to measure finely the temperature that is lower than 200℃ with aluminium coating.

FIBER OPTIC TEMPERATURE MEASURING SYSTEM

This paper presents a fiber optic temperature measuring system used for measuring the temperature in many occasions. The system is of reflective type and composed of thermostatic bimetal plate, lever piston framework, optical grating and optical fiber probes. When the temperature changes, the thermostatic bimetal plate deforms. Through lever piston framework, the optical grating produces displacement in the upright direction. Thus the change of the temperature is transformed into the upright displacement of the optical grating. Optical fiber probes are used for detecting the number of streak lines of the optical grating′s displacement depending on the change of temperature. The detected signal can be transmitted to the control center through optical fiber cable up to distance of 1 km. The measurable range of this system reaches 100℃ with accuracy of ±0.2℃.

Gamma-radiation effects in pure-silica-core photonic crystal fiber

We investigated the steady state gamma-ray radiation response of pure-silica-core photonic crystal fibers（PSC-PCFs）under an accumulated dose of 500 Gy and a dose rate of 2.38 Gy/min. The radiation-induced attenuation（RIA） spectra in the near-infrared region from 800 nm to 1700 nm were obtained. We find that the RIA at 1550 nm is related with hydroxyl（OH^-） absorption defects in addition to the identified self-trapped hole（STH） defects. Moreover, it is proposed and demonstrated that reduced OH^-absorption defects can decrease the RIA at 1550 nm. The RIA at 1550 nm has effectively declined from 27.7 d B/km to 3.0 dB/km through fabrication improvement. Preliminary explanations based on the unique fabrication processes were given to interpret the RIA characteristics of PSC-PCFs. The results show that the PSC-PCFs,which offer great advantages over conventional fibers, are promising and applicable to fiber sensors in harsh environments.

Fabry-Perot Temperature Sensor for Quasi-Distributed Measurement Utilizing OTDR

A quasi-distributed Fabry-Perot fiber optic temperature sensor array using optical time domain reflectometry （OTDR） technique is presented. The F-P sensor is made by two face to face single-mode optical fibers and their surfaces have been polished. Due to the low reflectivity of the fiber surfaces, the sensor is described as low Fresnel Fabry-Perot interferometer （FPI）. The working principle is analyzed using twobeam optical interference approximation. To measure the temperature, a certain temperature sensitive material is filled in the cavity. The slight changes of the reflective intensity which is induced by the refractive index of the material was caught by OTDR. The length of the cavity is obtained by monitoring the interference spectrum which is used for the setting of the sensor static characteristics within the quasi-linear range. Based on our design, a three point sensor array are fabricated and characterized. The experimental results show that with the temperature increasing from -30℃ to 80℃, the reflectivity increase in a good linear manner. The sensitivity was approximate 0.074 dB℃. For the low transmission loss, more sensors can be integrated.

Temperature and Salinity Dual-parameter Sensing Based on Forward Brillouin Scattering in 1060-XP SMF

A novel temperature and salinity discriminative sensing method based on forward Brillouin scattering(FBS)in 1060-XP single-mode fiber(SMF)is proposed.The measured frequency shifts corresponding to different radial acoustic modes in 1060-XP SMF show different sensitivities to temperature and salinity.Based on the new phenomenon that different radial acoustic modes have different frequency shift-temperature and frequency shift-salinity coefficients,we propose a novel method for simultaneously measuring temperature and salinity by measuring the frequency shift changes of two FBS scattering peaks.In a proof-of-concept experiment,the temperature and salinity measurement errors are 0.12℃and 0.29%,respectively.The proposed method for simultaneously measuring temperature and salinity has the potential applications such as ocean surveying,food manufacturing and pharmaceutical engineering.

Effect of Temperature and Gamma-Ray Irradiation on Optical Characteristics of Fiber Bragg Grating Inscribed Radiation-Resistant Optical Fiber

A new radiation-hard germano-silicate glass optical fiber with a pure silica glass buffer and a boron-doped silica glass inner cladding was fabricated for temperature sensor application based on the fiber Bragg grating(FBG)underg-ray irradiation environment.The temperature dependences of optical attenuation at 1550.5 nm and Bragg reflection wavelength shift from 18℃to 40℃before theγ-ray irradiation were about 4.57´10^(-4)dB/℃and 5.48 pm/℃,respectively.The radiation-induced optical attenuation at 1550.5 nm and the radiation-induced Bragg reflection wavelength shift under theγ-ray irradiation with the total dose of 22.85 kGy at 35℃were about 0.03 dB/m and 0.12 nm,respectively,with theγ-ray irradiation sensitivity of 5.25´10^(-3)pm/Gy.The temperature and theγ-ray irradiation dependence of optical attenuation at 1550.5 nm in the FBG written fiber with boron-doped silica glass inner cladding were about 6 times and 4 times lower than that in the FBG written fiber without boron-doped silica glass inner cladding under a temperature change from 18℃to 40℃and theγ-ray irradiation with the total dose of 22.85 kGy at 35℃,respectively.Furthermore,the effect of temperature increase on the Bragg reflection wavelength of the FBG written fiber with boron-doped silica inner cladding was much larger about 1000 times than that of theγ-ray irradiation.However,no influence on the reflection power of the Bragg wavelengths and the full width at half maximum(FWHM)bandwidth under temperature and theγ-ray irradiation change was found.Also,after theγ-ray irradiation with the dose of 22.85 kGy,no significant change in the refractive index was found but the residual stresses developed in the fiber were slightly relaxed or retained.

Miniature temperature sensor based on optical microfiber

Optical microfibers （OMs） are good alternatives in the field of sensing. In this letter, a simple and effective miniature temperature sensor based on OM is proposed and experimentally verified. Using pure water and fiber coating as the OM clad, an additional loss will occur due to the absorption of outer medium. The temperature of the outer environment can be estimated by monitoring the change in additional loss. In the demonstrated experiments, a series of OM with different diameters, waist lengths, and constructions are used as sensing elements. The correlation coefficients between the experimental results and the linear fittings are better than 0.99, and the temperature sensitivity obtained by the linear fittings can achieve -0.151 dB/℃ （in pure water） and -0.405 dB/℃ （covered by fiber coating）. Moreover, higher sensitivity can be obtained by decreasing the diameter, increasing the waist length of the OM, or choosing the proper operating wavelength.

Review of femtosecond laser fabricated optical fiber high temperature sensors [Invited]

The femtosecond laser has been an efficient tool for optical fiber high temperature sensor construction.Here,we review the progress of optical fiber high temperature sensors based on femtosecond laser fabricated fiber gratings and various types of fiber in-line interferometers in silica fibers and sapphire fibers.

BN/SiBCN light-leakage-proof coatings of silica optical fiber for long term sensors at high temperatures

SiBCN and BN/SiBCN light-leakage-proof coatings were prepared on silica optical fibers for sensing applications at high temperatures.Scanning electron microscopy was used to characterize the surface morphology and microstructure of the coated fiber.Mechanical and optical properties of the coated fiber were characterized by Raman,optical and tensile tests.Compared with the original fiber,the tensile strength of Si BCN and BN/Si BCN coated fiber show an increase of about 60%and 90%at room temperature,respectively.In addition,the tensile strength of BN/Si BCN coated silica optical fiber was increased by about 42%at 700°C.It has been found that the improvement of the strength of BN/Si BCN coated silica optical fiber is related to the healing of defects and residual compressive stress in fibers.From the light transmittance performance of the coated fiber,it was found that BN/Si BCN double coating could be an ideal total reflection solution to protect silica optical fiber from light leakage during high temperature sensing operation.