Sensitivity improvement of a humidity sensor based on silica nanospheres on a long-period fiber grating (original) (raw)
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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.
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.
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.
Recent Developments in Fiber Optics Humidity Sensors
Sensors, 2017
A wide range of applications such as health, human comfort, agriculture, food processing and storage, and electronic manufacturing, among others, require fast and accurate measurement of humidity. Sensors based on optical fibers present several advantages over electronic sensors and great research efforts have been made in recent years in this field. The present paper reports the current trends of optical fiber humidity sensors. The evolution of optical structures developed towards humidity sensing, as well as the novel materials used for this purpose, will be analyzed. Well-known optical structures, such as long-period fiber gratings or fiber Bragg gratings, are still being studied towards an enhancement of their sensitivity. Sensors based on lossy mode resonances constitute a platform that combines high sensitivity with low complexity, both in terms of their fabrication process and the equipment required. Novel structures, such as resonators, are being studied in order to improve the resolution of humidity sensors. Moreover, recent research on polymer optical fibers suggests that the sensitivity of this kind of sensor has not yet reached its limit. Therefore, there is still room for improvement in terms of sensitivity and resolution.
Sensors and Actuators B-chemical, 2007
Electrostatic self-assembly has been used in this work to fabricate a new optical fiber humidity sensor. Said sensor consists of a single-mode tapered fiber coated with a [PDDA/Poly R-478] nanostructured overlay, in such a way that the thickness can be controlled in order to optimize the sensor sensitivity, by stopping the deposition process at the maximum slope of the transmitted optical power. The same tapered optical fiber tested with an overlay coating at the optimal working point achieves 26.8 times better sensitivity than with a double thickness overlay. A variation of 16 dB in optical power is achieved with responses time of 300 ms for changes in relative humidity from 75% to 100%. The high dynamic performance and low temperature cross-sensitivity allows this sensor to be used for human breathing monitoring.
A Novel Optical Fiber Humidity Sensor Coated with Superhydrophilic Silica Nanoparticles
2011
This work presents an optical fiber based relative humidity sensor. Highly mono-dispersed and stable silica nanoparticles were synthesized by colloidal route. Layer by layer technique has been utilized to create ultrathin films of silica nanoparticles on the optical fiber end. This fabrication technique is a simple method based on the alternative immersion in oppositely charged colloidal solutions. The coated thin film of silica nanoparticles acts as nanometer-scale interferometric cavity. Sensor shows a high sensitivity and fast response towards relative humidity change.
Optical fiber long-period grating humidity sensor with poly(ethylene oxide)/cobalt chloride coating
Applied Optics, 2006
A long-period fiber grating (LPFG) humidity sensor is reported utilizing poly(ethylene oxide)/cobalt chloride (PEO/CoCl2) as a hybrid hygrosensitive cladding coating. A thin overlay of the material is deposited on the LPFG and with exposure to different ambient humidity levels, its spectral properties are modified. The material parameters associated with the sensing mechanism may include those of refractive index, absorption, and
Fiber optic long period grating sensors with a nanoassembled mesoporous film of SiO_2 nanoparticles
Optics Express, 2010
A novel approach to chemical application of long period grating (LPG) optical fibers was demonstrated, which were modified with a film nanoassembled by the alternate deposition of SiO 2 nanoparticles (SiO 2 NPs) and poly(diallyldimethyl ammonium chloride) (PDDA). Nanopores of the sensor film could be used for sensitive adsorption of chemical species in water, which induced the changes in the refractive index (RI) of the light propagating in the cladding mode of the optical fiber, with a concomitant effect on the transmission spectrum in the LPG region. The prepared fiber sensor was highly sensitive to the change in the RI of the surrounding medium and the response time was very fast within 10 s. In addition, chemical infusion into the film was tested using a porphyrin compound, tetrakis-(4-sulfophenyl)porphine (TSPP), which could be saturated within a few min. The lowest detectable concentration of the TSPP analyte was 10 µM. The TSPP infusion led to the development of well-pronounced dual resonance bands, indicating a large increase in the optical thickness of the film. The RI of the film was dramatically increased from 1.200 to ca. 1.540.
Measurement Science & Technology, 2011
A fibre-optic refractive index sensor based on a long period grating (LPG) with a nanoassembled mesoporous coating of alternate layers of poly(allylamine hydrochloride) (PAH) and SiO2 nanospheres was demonstrated. PAH/SiO2 coatings of different thicknesses were deposited onto an LPG operating near its phase matching turning point in order to study the effect of the film thickness and porosity on sensor performance. Three aqueous solutions of ethanol, glucose and sucrose of different concentrations were used to allow characterization of the refractive index (RI) over a wide RI range (1.3330-1.4906). The device showed a high sensitivity (1927 nm/refractive index unit) to RI changes with a response time less than 2 s. In particular, the current study suggested that the low RI of the mesoporous film, 1.20 at 633 nm, facilitates the measurement of external indices higher than that of the cladding, extending the range of operation of LPG-based RI sensors. The ability of this device to monitor, in real time, RI changes during a dilution process is demonstrated and discussed.
Relative Humidity Sensor Based on Tapered Optical Fiber Coated with Silica-Gel
2020
We have fabricated and characterized a relative humidity (RH) sensor, by tapering the mid-region of a piece of multimode-fiber (MMF) and coating it with a layer of silica-gel as the sensing layer. The experimental results show that the device sensitivity depends on the presence of silica-gel layer. The sensor response to the fluctuations of relative humidity in the environment is determined through measuring the changing in fiber transmission power. The experimental results also show that the device sensitivity increases as the diameter of the fiber, in the tapered region, decreases down to a certain size. The same results show that the highest linear sensitivity of 0.39 dB/%RH can be achieved for a tapered region of the MMF with 4-μm waist diameter coated with silica gel.