Recent Developments in Fiber Optics Humidity Sensors (original) (raw)
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Lossy mode resonances toward the fabrication of optical fiber humidity sensors
Measurement Science and Technology, 2012
In this work, the fabrication and characterization of novel humidity sensors based on lossy mode resonances (LMRs) are presented. Indium tin oxide (ITO) and In2O3 coatings fabricated onto an optical fiber are used as the LMR supporting coatings. Poly-acrylic acid and polyallylamin hydrochloride polymeric coatings were used as the sensitive layers. A comparative study between the ITO and the In2O3
Measurement Science and Technology, 2009
A novel sensing configuration for measuring humidity based on a long-period fibre grating coated with a thin film of silica nanospheres is proposed. The polymeric overlay is deposited on the grating using the electrostatic self-assembly technique. This thin film changes its optical properties when exposed to different humidity levels that translate into a shift of the resonance wavelength of the fibre grating. Wavelength shifts up to 12 nm in a relative humidity range from 20% to 80% are reported, and it is further demonstrated that such humidity sensitivity has negligible thermal dependence.
Humidity sensor based on a long-period fiber grating coated with a hydrophobic thin film
SPIE Proceedings, 2010
In this work it is proposed a novel fiber optic humidity sensor based on a functionally coated long-period fiber grating (LPG). The coating is composed of tetraorthosilicate matrix functionalized with perfluorooctyltriethoxysilane and its fabrication was performed by the sol-gel technique using a dip coating process using the LPG as substrate. The fabricated sensor was tested in a programmable temperature and climatic chamber. Relative humidity (RH) was varied in range from 20%RH to 80%RH at room temperature. The results showed a smooth exponential-like wavelength shift of the LPG attenuation band. ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS ACKNOWLEDGEMENTS This work was funded in part by the Spanish Ministry of Education and Science-FEDER Research Grant TEC2009-09210 CONCLUSIONS CONCLUSIONS CONCLUSIONS We propose a new HR sensor based on a coated LPG. The hydrophobic sensitive overlay was fabricated using the sol-gel technology. The sensitive overlays have been successfully placed onto the LPG with a strong hydrophobic behavior.
Two-Layer Nanocoatings in Long-Period Fiber Gratings for Improved Sensitivity of Humidity Sensors
IEEE Transactions on Nanotechnology, 2000
A relative humidity sensor based on the deposition of electrostatic self-assembled alumina (Al 2 O 3 )a nd poly(sodium 4-styrenesulfonate) on the cladding of a long-period fiber grating (LPFG) has been designed. The sensitive material has a lower refractive index than that of the fiber cladding, which limits the sensitivity of the LPFG response. In order to enhance its sensitivity, a previous high refractive index coating has been deposited. The overlay thickness is of the order of magnitude of the light wavelength used to interrogate the sensor. A theoretical model of multilayer cylindrical waveguides based on coupled-mode theory has been used to predict the phenomenon. Experimentally, an increased wavelength shift of the attenuation bands (75%) was obtained during the fabrication of the sensor, and, what is more important, the sensitivity was improved by a ratio of almost four.
Analysis of the Relative Humidity Response of Hydrophilic Polymers for Optical Fiber Sensing
Polymers, 2022
Relative humidity (RH) monitorization is of extreme importance on scientific and industrial applications, and optical fiber sensors (OFS) may provide adequate solutions. Typically, these kinds of sensors depend on the usage of humidity responsive polymers, thus creating the need for the characterization of the optical and expansion properties of these materials. Four different polymers, namely poly(vinyl alcohol), poly(ethylene glycol), Hydromed™ D4 and microbiology agar were characterized and tested using two types of optical sensors. First, optical fiber Fabry–Perot (FP) tips were made, which allow the dynamical measurement of the polymers’ response to RH variations, in particular of refractive index, film thickness, and critical deliquescence RH. Using both FP tips and Long-Period fiber gratings, the polymers were then tested as RH sensors, allowing a comparison between the different polymers and the different OFS. For the case of the FP sensors, the PEG tips displayed excellent ...
Sensors (Basel, Switzerland), 2009
This work addresses a new configuration that improves the sensitivity of a humidity sensor based on a long-period fiber grating coated with a SiO(2)-nanospheres film. An intermediate higher refractive index overlay, deposited through Electrostatic Self-Assembly, is placed between the fiber cladding and the humidity sensitive film in order to increase the total effective refractive index of the coating. With this intermediate design, a three-fold improvement in the sensitivity was obtained. Wavelength shifts up to 15 nm against 5 nm were achieved in a humidity range from 20% to 80%.
Performance Analysis of Humidity Tapered Optical Fiber Sensor
Research Square (Research Square), 2022
Among different interferometric fiber optic sensors a Relative Humidity sensor based on a singlemode-no-core-singlemode tapered fiber structure is proposed. The mathematical model of the interferometer structure is developed, simulated and validated as a refractive index sensor. Different materials for coating the No-core fiber section are analyzed for better Relative Humidity sensitivity. Agarose, Porous Silica and SiO2 nanoparticles were selected as coating materials for Pure Silica and d-PMMA fibers. The d-PMMA fiber with Agarose coating presents the highest average sensitivity of 533.46pm/RH% in the 0-60% RH range, when the tapered section has zero length. Furthermore, variations in the dimensions of the structure are explored showing that we can tune the sensitivity according to the tapered length and radius. An extension of the tapered section up to 4000µm gives an improvement of 227% in the average sensitivity. Moreover, a reduction of the tapered radius from 15µm to 1.5µm gives an rise in the sensitivity of 295%.
Polyvinyl alcohol–coated hybrid fiber grating for relative humidity sensing
Journal of Biomedical Optics, 2011
A relative humidity (RH) sensor based on a hybrid fiber grating coated with polyvinyl alcohol is proposed and demonstrated experimentally. The hybrid fiber grating is formed by superimposing a normal fiber Bragg grating (FBG) and a tilted-FBG around the same position of a single-mode fiber so that it can work in the reflection mode. Optical power of the reflected signal changes with the refractive index of the moisture sensitive polyvinyl alcohol, and humidity measurement can be realized. Experimental results show that the measurement range is 30 to 95% with the maximum sensitivity of 0.737 nW/% RH. The average response time is ∼2 s and the measurement is nearly insensitive to temperature. Compared with the wavelength detection method used in normal FBG-based relative humidity sensors, the intensity demodulation method in this report is simpler and more cost-efficient.