The sensing properties of zinc oxide (ZnO) combined with tilted fiber Bragg gratings have been studied in this work for the development of organic vapor optical fiber sensors. ZnO has been deposited onto tilted optical fiber Bragg gratings by drop casting technique to obtain coatings with thickness below 100nm. For a title angle of 4°, cladding modes up to 4 dB peak to peak amplitude were obtained and, as a consequence, the fundamental mode strength dropped below 0.5dB. The sensing features were evaluated by exposing the sensor to saturated atmospheres of three different alcohols and acetone. A negligible change was registered for methanol but in the case of ethanol and isopropanol a 24pm red shift was observed; in the case of acetone, the shift was 96pm which is of the order of spectral width of certain cladding modes. For all cases, the shifts were reversed once the organic vapors were removed. Ongoing studies are focused on the optimization of the sensing layer as well as the tilted angle to enhance the spectral response of the sensor.
In this paper, a new multipoint optical fiber system for relative humidity measurements based on SnO2-FP (Fabry-Pérot) sensing heads and an optical interrogator as single active device is presented and characterized. The interrogation of the sensing heads is carried out by monitoring the Fast Fourier Transform phase variations of the FP (Fabry-Pérot) interference frequencies. This method allows to multiplex several sensors with different wavelength spacing interference pattern. The sensors operate within a wide humidity range (20%–90% relative humidity) with low crosstalk between them. Five sensing heads have been measured using two different channels of the optical interrogator. The availability of four channels in the interrogator allows to multiplex a higher number of sensors, reducing proportionally the cost of each sensing point.
In this paper, a new sensor system for relative humidity measurements based on a SnO2 sputtering deposition on a microstructured optical fiber (MOF) low-finesse Fabry-Perot (FP) sensing head is presented and characterized. The interrogation of the sensing head is carried out by monitoring the Fast Fourier Transform phase variations of the FP interference frequency. This method is low-sensitive to signal amplitude variations and also avoids the necessity of tracking the evolution of peaks and valleys in the spectrum. The sensor is operated within a wide humidity range (20%-90% relative humidity) with a maximum sensitivity achieved of 0.14rad/%. The measurement method uses a commercial optical interrogator as the only active element, this compact solution allows real time analysis of the data.
An optrode able to detect glucose dissolved in water has been implemented. The device is based on the luminescence emission of a Molecularly Imprinted Polymer synthesized specifically for glucose detection, therefore its intensity changes in presence of glucose. This sensing material is attached onto a cleaved ended polymer-clad optical fibre and it is excited by light via 1x2 fibre coupler. The reflected fluorescence signal increases when it is immersed into glucose solutions and recovers to the baseline when it is dipped in ultrapure water. This reversible behaviour indicates the measurement repeatability of using such a glucose sensor.
An experimental comparison of the stability performance of two different optical multiwavelength lasers is shown based
on erbium highly doped fiber amplification. The two laser structures compared were: a star configuration using a 2x4
coupler to extract the signal from the ring to 4 FBGs and a structure with 4 active ring resonators that use both the same
pump laser. Both lasers use Fiber Bragg gratings (FBG) to select the operation wavelengths within the resonant ring
cavity.
The stability of this new laser is compared with the achieved by a single ring configuration. The improvement of both
stabilities depending on the time and temperature for the new structure was experimentally demonstrated.
The utilization of the new configuration for multiplexing optical fiber sensors has also been carried out. The sensors
provide amplitude modulation in response to the curvature introduced by a temperature-sensitive element. Each sensor is
identified by a different wavelength generated by each FBG. The signal generated by the grating firstly is used as
reference signal ant secondly is launched towards the sensors and the transmitted signal is measured. The sensors show a
stable and linear response when measurements are carried out using simultaneously all the outputs of the structure for
transmitting the multiple wavelengths to the sensors and utilizing the serial referencing output of the laser.
We propose a hybrid network that combine point and distributed Brillouin sensors in an architecture that also deploys
remote distributed Raman amplification to extend the sensing range. A 46-km proof-of-concept network is
experimentally demonstrated integrating point vibration sensors based on fiber-optic tapers, with distributed temperature
sensing along the network bus. The sensor network with a double-bus topology offers a higher optical signal to noise
ratio and dynamic range than a single-bus for intensity point multiplexed sensors. In this network, we include low-cost
intensity sensors that are able to measure vibrations in the 0.01 to 50 Hz frequency range, which are important in the
monitoring of large infrastructures such as pipelines.
In this work, a novel CWDM (Coarse Wavelength Division Multiplexing) network that multiplexes intensity modulated
optical fibre sensors is presented. These transducers are based on a sensing material that suffers reversible changes in its
optical properties in presence of organic vapours. This compound is fixed onto cleaved ended single mode optical fibres
pigtails using Electrostatic Self-Assembly method. As their response depends on intensity changes, a referencing signal
is simultaneously generated to eliminate the effect of optical source power fluctuations. Thus, a parallel array of phaseshifted
fibre Bragg gratings (PS-FBGs) is included to obtain the referencing signal. Looking forward to remote sensing
applications, an Erbium doped fibre amplifier (EDFA) is included in the header of the network to reach up to 4 km of
distance. Four new sensors have been multiplexed and exposed to saturated atmospheres of methanol and ethanol
individually, showing different response and recovery times in each case. Finally, we checked that our sensors were able
to distinguish between pure and kerosene polluted water probes in terms of response and recovery times as well.
This paper presents the application of a new erbium-doped fiber ring laser configuration for the multiplexing
of intensity sensors. The proposed scheme exploits two separated branches to generate simultaneous emission
at four different wavelengths. Fiber Bragg gratings are used to select the operating wavelengths within the
erbium-doped fiber ring. The first branch presents a serial configuration to generate the reference lasers. The
second branch exploits a tree configuration and includes the optical intensity temperature sensors. A comparison
between both branches of the same setup is carried out, and their temperature and time stability is shown by
varying the erbium doped fiber.
A new amplified CWDM (Coarse Wavelength Division Multiplexing) self-referencing sensor network using phase-shifted
fiber Bragg gratings (PS-FBGs) is experimentally demonstrated in this work. The network uses the PS-FBGs to
address intensity sensors in a transmissive configuration, obtaining simultaneously in reflection a wavelength encoded
reference signal. In order to enable the remote operation of the sensors, we have introduced optical amplification at the
interrogation header of the network, using highly doped erbium fiber.
A novel vapochromic complex has been used to develop an optical fiber device sensitive to pyridine vapors. In solid
state, this material is blue, and in the presence of pyridine vapors, its color changes to pink-white. The vapochromic
material is solved in tetrahydrofuran (THF) and immobilized in a plasticized polymeric, fixing it onto a cleaved ended
optical fiber pigtail by dip coating. The fabrication process was optimized in terms of number of dips and dipping speed,
evaluating the final devices by dynamic range. Employing a reflection set up, the response of the sensors was registered
in terms of absorbance spectrum and changes in reflected optical power. Devices showing a linear response with
different vapors concentrations were obtained, with a detection limit of 1 PPM (v/v).
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