A visible fiber Bragg grating (Vis-FBG) with wavelength peak centered at 673.07 nm was inscribed in a multimode fiber designed for infrared (IR) operation using a femtosecond (fs) laser emitting at 248 nm. The fiber cladding is removed by chemical etching in hydrofluoric acid solution (40%). The sensor refractive index response is determined by dipping the sensor into diluted glycerin solution at different concentrations with refractive index range from 1.3328 to 1.4607. The Vis-FBG performance is compared with an IR etched FBG (EFBG) with similar diameter. The sensitivity found for the Vis-FBG sensor is 15.71nm/RIU with a 6.34 x 10-3 RIU resolution for a refractive index of 1.4607.
We report an optical fiber multiparameter sensor for refractive index and temperature measurements. The proposed sensor is composed by a microcavity in multimode fiber, assisted by Bragg gratings (FBGs) in singlemode fiber. The microcavity is engraved in a multimode optical fiber by using the femtosecond laser micromachining. The sensor is characterized through microcavity immersion in water and based on its temperature variation. The results show that it is possible to obtain refractive index and temperature measurements with sensitivities of 1625 μW/RIU (refractive index unit) and of 0.23 μW/°C, with resolution of 1.8 × 10-4 RIU and of 1.3°C.
In this work a refractometric sensor for assessment of methanol presence in biodiesel is reported. The transducer relies on the interference between the forward and back propagating modes of a single long period grating, written close to an end-face mirror optical fiber. The sensing method is thermally assisted in order to overcome the drawback caused by the high refractive index (close to the fiber cladding index) of methanol-biodiesel blends at low temperatures. Sensor showed a combined standard uncertainty of 0.6 % v/v of methanol in biodiesel for a confidence level of 68.27%, within the methanol concentration ranging from 0 to 25 % v/v.
This work describes two approaches for refractometric sensors based on cascaded long period gratings for evaluating
substances with refractive indices equal to or higher than the fiber cladding at room temperature. The devices are
experimented on the assessment of fuel quality regarding the presence of remaining vegetable oil in biodiesel, as well as
to determine the concentration of biodiesel in the biodiesel-petrodiesel blends.
Experimental and numerical demonstration of the acousto-optic effect applied in long period grating by means of
flexural waves is presented. The interaction between acoustic and optical waves is modeled with help of the method of
assumed modes, which delivers the strain field inside the grating and the transfer matrix method, which, given the strain
field as input, calculate the resultant grating spectrum. The experimental and theoretical results are found to be in good
agreement. The main effect of the bends in the grating is the break of degeneracy of the circular cladding modes, leading
the attenuation band to be changed. Among all the applications of this methodology, it is important to mention the
possibility of use as a tunable filter, laser cavity gain controller, switching device and transducer in sensing systems.
This paper describes an approach to identify, quantify and express uncertainties in optical fiber grating sensor
measurements, based on the International Standard Organization's Guide to the Expression of Uncertainty in
Measurement. The proposed approach was used to evaluate the uncertainties in the measurements performed with both a
fiber Bragg temperature sensor and a long period grating refractometric sensor.
This work presents a sensing system based on an etched fiber Bragg grating, applied to the refractometric analysis of
water-ethanol mixtures. The system configuration employs one etched-FBG operating at two temperatures, (20.0 ± 0.5)
°C and (3.0 ± 0.5) °C. The sensing system performance in measuring the ethanol-water proportions is evaluated in the
concentration range between 0.0 and 100.0 % v/v of water in ethanol, resulting in uncertainties less than 3.9 % v/v. The
sensor capability to determine the ethanol concentration is shown, even for the range of concentrations where the
correlation between refractive index and ethanol proportion in the sample presents an ambiguous behavior.
In this work we studied the behavior of an in fiber Mach-Zehnder interferometer for salinity measurements. The salt
species used are KCl, NaCl e NaCOOH (organic salt) within the concentration range from 3 g.L-1 to 150 g.L-1. The
results are compared with traditional salinity measurement methods (conductivity and refractive index) and show that the
device can distinguish and identify the concentration of each species saline.
The influence of temperature in the measurements of surrounding refractive index using long-period fiber gratings is
studied for room temperature variations. For temperature changes close to 2°C it is verified wavelength shifts lower than
0.1 nm for the grating immersed in air and as high as 1.1 nm for a hydrocarbon sample whose refractive index is 1.4530.
Sensitivity evaluations of long-period fiber gratings and evanescent fiber sensors require a temperature system control
that keeps the temperature constant. Otherwise, it should be considered compensation systems that consider not only the
temperature changes but also the refractive index and the thermal-optical coefficient of the materials under analysis.
This work shows the application of an optical sensor to detect the presence of Cr(III) and Cr(VI) oxidation states in water solutions. The sensing device is a long period grating produced in a standard telecommunication optical fiber by applying a suitable number of point-to-point electrical arc discharges from a fusion splicer. In order to analyze the Cr(III) and Cr(VI) solutions, the sensing device is kept into a recipient under constant longitudinal stress and the Chromium solution samples are added to it. The results show that the sensor can not only detect the presence, but also differentiate between the two-oxidation states. Samples with Chromium concentrations from 0.16 mg/l to 5.2 mg/l are analyzed, leading to maximum wavelength shifts (relative to the LPG in pure water) of 0.14 nm and 0.26 nm for Cr(III) and Cr(VI), respectively. A comparison between the results obtained for both solutions shows that is possible to identity any of the Chromium oxidation states present in the sample until a lower limit concentration of 2.6 mg/l for the employed set-up.
Fiber Optic Bragg Grating Sensors are modeled and studied in high birefringence fiber. Coupled mode theory and multilayer approach are used to predict the spectral characteristics of the structure. Results are compared with experimental characterization of devices produced by UV light using the external method.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.