Passive temperature compensation of piezo-tunable fibre Bragg gratings (original) (raw)
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Passive Temperature-Compensating Technique for Microstructured Fiber Bragg Gratings
IEEE Sensors Journal, 2008
The thermal drift of the characteristic wavelength of fiber Bragg gratings (FBGs) photowritten in the core of microstructured fibers (MOFs) is significantly reduced by inserting a liquid of suitable refractive index into their holes. For instance, the spectral range of variations is divided by a factor of 4 over a temperature range larger than 20°C in a 6-hole MOF, and the maximum sensitivity is reduced. Such passive FBG temperature compensation technique is of great interest for applications involving accurate sensing free of thermal effects.
Response characteristics of thin-film-heated tunable fiber Bragg gratings
IEEE Photonics Technology Letters, 2000
We investigate the thermal response of a tunable fiber Bragg grating (FBG) with a metal coating on bare fiber surface as a heater both theoretically and experimentally. By solving a differential equation of temperature as a function of time, together with some reasonable approximation, we obtained an explicit description of the thermal response characteristics with the structure's heat capacity and a time constant as its parameters. Using a squared wave modulation current and a tunable laser, we measured the temporal response of the tunable FBG. The obtained response curves match our solution. A time constant in the range of subseconds was deduced. Discussions on the tuned FBG spectra are also given at the end to explain the linewidth broadening effect at higher temperature.
Applied Optics, 2013
This paper presents an experiment and analysis on the factors affecting nonlinear evolution of Bragg wavelength with change in temperature in typical bare and embedded fiber Bragg grating-based (FBG) temperature sensors. The purpose of the study was to find the constants in the function required to evaluate temperature from Bragg wavelength shift. The temperature sensitivity of bare FBGs was found to increase with temperature elevation, and is different for FBGs written in different fiber types. The average temperature sensitivity increased by about 20% when the bare FBG temperature was elevated from 25°C to 525°C. The average temperature sensitivity of the embedded FBG sensor, investigated in the temperature range of 30°C-90°C, was a factor of 2-3 times larger than for bare FBG, depending on its fastened length with the substrate. Analytically, it is shown that the nonuniform behavior of temperature sensitivity in bare FBGs is the result of both the thermal expansion effect of the fiber and the temperature derivatives of the effective refractive index. The strain transfer and temperature coefficients of thermal expansion of the substrate affect the nonuniform behavior of temperature sensitivity in embedded FBG sensors.
Sensors, 2012
To compensate for the temperature dependency of a standard FBG, a cladding-etched FBG immersed with a liquid mixture having a negative thermo-optic coefficient is presented, and its characteristics are investigated. The Bragg wavelength of the cladding-etched FBG is shifted counter to the direction of the Bragg wavelength shift of a conventional FBG according to the mixing ratio of glycerin to water; thus, the temperature-dependent Bragg wavelength shift was almost compensated by using a liquid mixture of water (50%) and glycerin (50%) having the negative thermo-optic coefficient of −5 × 10 −4 °C −1 .
Fiber Bragg gratings for low-temperature measurement
Optics Express, 2014
We demonstrate the use of fiber Bragg gratings (FBGs) as a monolithic temperature sensor from ambient to liquid nitrogen temperatures, without the use of any auxiliary embedding structure. The Bragg gratings, fabricated in three different types of fibers and characterized with a high density of points, confirm a nonlinear thermal sensitivity of the fibers. With a conventional interrogation scheme it is possible to have a resolution of 0.5 K for weak pure-silica-core FBGs and 0.25 K using both boron-doped and germanium-doped standard fibers at 77 K. We quantitatively show for the first time that the nonlinear thermal sensitivity of the FBG arises from the nonlinearity of both thermo-optic and thermal expansion coefficients, allowing consistent modeling of FBGs at low temperatures.
Fiber Bragg Grating Temperature Sensor
2000
In this paper, we analyze theoretically and experimentally the performance of fiber Bragg gratings as temperature sensors. These sensors have potential applications in monitoring the temperature in aerospace structures and smart
Modeling and Simulation of Fiber Bragg Grating as Temperature Sensor
This paper deals with mathematical modeling, design and application of Fiber Bragg Grating as temperature sensor .In this paper we used the MATLAB and filter characteristics simulation software as a tools for simulation results. The fabrication of Fiber Bragg Grating, their characteristics and fundamental properties are described. The reflectivity of FBG is described using simulation results. This paper also present the simulation results of FBG as temperature and gas sensor. From the plotting analysis it can be concluded that for reduce the width of reflection spectrum we can take long grating.
IEEE Photonics Journal, 2012
This paper presents a novel structure based on bimetallic strips for enhancing temperature sensitivity of fiber Bragg grating (FBG) sensors. Two different types of sensor heads have been designed for this implementation. The first sensor head consists of an FBG that is fixed between ceramic block on one side and a bimetallic strip made up of aluminum and copper on the other. The second sensor head consists of an FBG that is fixed between two bimetallic strips. Theoretical and experimental studies carried out on these proposed sensor heads resulted in an increase in temperature sensitivity of about six times greater than that of bare FBG sensor. Further, the proposed sensors have shown good linearity and stability.
Quadratic Behavior of Fiber Bragg Grating Temperature Coefficients
Applied Optics, 2004
We describe the characterization of the temperature and strain responses of fiber Bragg grating sensors by use of an interferometric interrogation technique to provide an absolute measurement of the grating wavelength. The fiber Bragg grating temperature response was found to be nonlinear over the temperature range Ϫ70°C to 80°C. The nonlinearity was observed to be a quadratic function of temperature, arising from the linear dependence on temperature of the thermo-optic coefficient of silica glass over this range, and is in good agreement with a theoretical model.
IEEE Transactions on Instrumentation and Measurement, 1997
A major problem currently affecting the implementation of in-fiber refractive-index grating-based optical fiber devices is the drift in wavelength modulation due to the change in the ambient temperature. For accurate and reliable long-term operation of these devices, suitable temperature compensation techniques are a necessity. This paper presents a novel temperature compensation technique for in-fiber refractive index grating-based devices and components. The proposed technique is based on the temperature-dependent spectral characteristics of a dielectric multilayer thin-film interference filter fabricated on the endface of refractive-index grating impressed optical fiber. Temperature compensation is achieved by comparing the reflected intensities at the grating-reflected and the interference filterreflected wavelengths. The proposed scheme also compensates for light source fluctuations and lead-in fiber bending losses.