Marc Debliquy

Hybrid fiber gratings coated with a catalytic sensitive layer for hydrogen sensing in air

Using hydrogen as fuel presents a potential risk of explosion and requires low cost and efficient leak sensors. We present here a hybrid sensor configuration consisting of a long period fiber grating (LPFG) and a superimposed uniform fiber Bragg grating (FBG). Both gratings are covered with a sensitive layer made of WO(3) doped with Pt on which H(2) undergoes an exothermic reaction. The released heat increases the temperature around the gratings. In this configuration, the LPFG favors the exothermic reaction thanks to a light coupling to the sensitive layer while the FBG reflects the temperature change linked to the hydrogen concentration. Our sensor is very fast and suitable to detect low hydrogen concentrations in air whatever the relative humidity level and for temperatures down to -50 degrees C, which is without equivalent for other hydrogen optical sensors reported so far.

Catalytic Fiber Bragg Grating Sensor for Hydrogen Leak Detection in Air

The explosion risk linked to the use of hydrogen as fuel requires low-cost and efficient sensors. We present here a multipoint in-fiber sensor capable of hydrogen leak detection in air as low as 1% concentration with a response time smaller than a few seconds. Our solution makes use of fiber Bragg gratings (FBGs) covered by a catalytic sensitive layer made of a ceramic doped with noble metal which, in turn, induces a temperature elevation around the FBGs in the presence of hydrogen in air.

Silicon-on-Insulator (SOI) Ring Resonator-Based Integrated Optical Hydrogen Sensor

We demonstrate a novel, highly sensitive integrated hydrogen sensor based on a silicon ring resonator on the silicon-on-insulator platform. The hydrogen sensitive element in the sensor structure is a platinum-doped tungsten oxide catalytic coating. The catalytic combustion of hydrogen in air leads to a local temperature rise in the ring resonator. The resulting thermo-optic effect shifts the ring resonator resonance. Resonance wavelength shifts higher than a nanometer are measured for hydrogen concentrations below the 4% lower explosion limit. A potentially tunable sensitivity of around 480 pm shift per %H2 is achieved at an operating temperature of about 40degC.

Influence of atmospheric pollutants on the conductance of phthalocyanine films

Abstract Molecular oxygen has always been considered as the main gaseous agent responsible for the doping of intrinsically insulating phthalocyanine thin films. In this paper, it is shown that oxygen has only a relatively minor effect on electrical conductance and that traces (

High-refractive-index transparent coatings enhance the optical fiber cladding modes refractometric sensitivity

The high order cladding modes of standard single mode optical fiber appear in quasi-degenerate pairs corresponding to mostly radially or mostly azimuthally polarized light. In this work, we demonstrate that, in the presence of a high-refractive-index coating surrounding the fiber outer surface, the wavelength spacing between the orthogonally polarized cladding modes families can be drastically enhanced. This behavior can be advantageously exploited for refractometric sensing purposes. For this, we make use of tilted fiber Bragg gratings (TFBGs) as spectral combs to excite the orthogonally polarized cladding modes families separately. TFBGs were coated with a nanometer-scale transparent thin film characterized by a refractive index value close to 1.9, well higher than the one of pure silica. This coating brings two important assets: an ~8-fold increase in refractometric sensitivity is obtained in comparison to bare TFBGs while the sensitivity is extended to surrounding refractive index (SRI) values above 1.45.

A Formaldehyde Sensor Based on Molecularly-Imprinted Polymer on a TiO2 Nanotube Array

Today, significant attention has been brought to the development of sensitive, specific, cheap, and reliable sensors for real-time monitoring. Molecular imprinting technology is a versatile and promising technology for practical applications in many areas, particularly chemical sensors. Here, we present a chemical sensor for detecting formaldehyde, a toxic common indoor pollutant gas. Polypyrrole-based molecularly-imprinted polymer (PPy-based MIP) is employed as the sensing recognition layer and synthesized on a titanium dioxide nanotube array (TiO2-NTA) for increasing its surface-to-volume ratio, thereby improving the sensor performance. Our sensor selectively detects formaldehyde in the parts per million (ppm) range at room temperature. It also shows a long-term stability and small fluctuation to humidity variations. These are attributed to the thin fishnet-like structure of the PPy-based MIP on the highly-ordered and vertically-aligned TiO2-NTA.

Functional Layers for Zn II Ion Detection: From Molecular Design to Optical Fiber Sensors

We report on the synthesis of a novel perylene monoimide derivative that shows high response and selectivity for zinc ion detection. The complexation of Zn(2+) by the dye is followed by FD-MS, (1)H NMR, UV-vis spectroscopy, and isothermal titration calorimetry. Quantum chemical calculations are performed to gain further insight into the electronic processes responsible for the spectroscopic changes observed upon complexation. Finally, the perylene dye is incorporated in a sol-gel silica layer coated on optical fibers that are then used for Zn(2+) detection in aqueous solution.

Infrared radiation detector using a pair of fiber Bragg gratings

A novel infrared radiation detector based on a pair of fiber Bragg gratings (FBGs) is described. In the proposed configuration, the two FBGs are distant by a few centimeters and are characterized by Bragg resonances separated by a few nanometers. One FBG of the pair is coated with an IR-absorbing layer which converts the radiation into heat. Therefore, exposure to IR radiations will increase the temperature of the coated FBG, which in turn induces a Bragg wavelength shift to higher values. To take into account the ambient temperature fluctuations, the second grating is protected by an IR-reflecting tube which prevents heating of this grating that can then be used as temperature reference. IR radiation measurements are finally obtained through the monitoring of the differential shift between both Bragg wavelengths. This shift shows a monotonic behavior as a function of the IR radiations. This sensor shows a strong potential for early fire detection as it detects radiation emitted during the fire instead of the temperature increase when the fire is fully developed.

Infrared Radiation Detection With Matched Fiber Bragg Gratings

In this letter, a novel infrared (IR) radiation detector is proposed for early fire detection. It consists of two matched apodized fiber Bragg gratings (FBGs) cascaded in a single optical fiber and separated by a few centimeters. One of the gratings is covered with an IR-absorbing layer that converts the radiation into heat while the second FBG provides a temperature reference. To obtain a fast and cost-effective detector, the demodulation technique consists in measuring the total reflected power, which monotonically evolves in a range of flux that depends on the FBGs spectral characteristics. With the 24-mm-long Gaussian apodized FBGs used in this work, we report a mean sensitivity of 7 nW/(W/m2) in the range 0-3000 W/m2.

Review of the Use of the Optical Fibers for Safety Applications in Tunnels and Car Parks: Pollution Monitoring, Fire and Explosive Gas Detection

Optical fiber sensors bring to measurement systems all the advantages offered by the optical fiber technology. The potential applications for these sensors are numerous and can spread from medical diagnosis to pipe line monitoring passing through geological measurements. This chapter will focus on the applications in road tunnels and undercroft car parks monitoring. It will detail the existing optical fiber sensor methods, commercially available or under development in the field of air quality monitoring, in particular NO2 that is representative of toxic automotive pollution, flaming fire detection and combustible gas leak detection (in particular methane and hydrogen).