Henri Gagnaire

Surface plasmon resonance hydrogen sensor using an optical fibre

An optical fibre surface plasmon resonance (SPR) sensor has been developed for the detection of hydrogen leakages. A thin palladium layer deposited on the bare core of a multimode fibre was used as the transducer. In this device, modification of the SPR is due to variation in the complex permittivity of palladium in contact with gaseous hydrogen. This effect is enhanced by using selective injection of high-order modes in the fibre via a collimated beam with non-normal incidence on the input end of the fibre. Measurements of concentrations as low as 0.8% of hydrogen in pure nitrogen have been found to be possible. The response time varies between 3 s for pure hydrogen and 300 s for the lowest concentrations. Such a large range can be explained by the two different crystallographic phases of the palladium-hydrogen system. Moreover, the response of the sensor is dependent on the length of the sensing area. In preliminary experiments, it has been possible to split the sensing area in order to achieve a two-point detection device.

The effects of polarization of the incident light-modeling and analysis of a SPR multimode optical fiber sensor

A 3D skew ray modeling has been developed to consistently explain the experimental phenomena for an intrinsic SPR multimode optical fiber sensor. The effects of the polarization direction of the incident light at certain conditions have been clarified. This simulation is needed to accurately detect the variations of the refractive index of the bulk medium and of the thickness of the thin surface layer. More complete knowledge about light energy transmission by the skew ray in the multimode step-index fiber is obtained by this investigation.

Optical fibre sensor coated with porous silica layers for gas and chemical vapour detection

Fibre optic sensors have been conceived in new technologies for detecting very small amounts of chemical, gaseous and biological species. Recently, new polymer-clad silica (PCS) fibres coated with thin porous silica layers have been developed. These porous layers have been prepared by the sol-gel method using the dip-coating technique. In this work, this new material has been investigated for detecting gases and vapours. By choosing a fixed incident angle, variation of light power transmitted through the fibre is detected as the vapour or gas to be detected is sorbed in the porous silica layer. Good sensitivity and reversibility have been obtained for this system. Moreover, both the response time and the desorption time have been found less than 2 min. Chlorinated hydrocarbons such as trichloroethylene, carbon tetrachloride, chloroform, dichloromethane and alkanes such as propane, butane and hexane can be detected with detection limits of 0.6, 1.5, 1.7, 4, 25, 10 and 5% respectively.

Surface plasmon resonance fibre-optic sensor for gas detection

Surface plasmon resonance (SPR) is a powerful technique for direct sensitive (bio)chemical detection. In this work, a surface plasmon resonance fibre-optic sensor has been developed allowing sensitive remote detection. A 50 nm thick silver film is deposited by thermal evaporation onto the silica core of the optical fibre. To protect the silver from oxidation, self-assembled monolayers (SAMs) of long-chain alkanethiols are used. For detecting gas and vapours, the surrounding dielectric medium consists of polyfluoroalkylsiloxane, deposited on the modified metallic film. Halogenated hydrocarbons such as trichloroethylene, carbon tetrachloride, chloroform and methylene chloride have been tested with detection limits of 0.3, 0.7%, 1 and 2%, respectively. Moreover, both the response time and the desorption time are less than 2 min.

Development of a fiber-optic sensor based on surface plasmon resonance on silver film for monitoring aqueous media

Abstract A reliable fiber-optic SPR sensor based on silver is developed in this paper for chemical and biological applications. The range of measurable indices is shifted down by coating an overlay of zirconium acetate on the silver surface by sol–gel technique. The feasibility has been investigated in advance by theoretical analyses. The experimental fiber-optic sensor demonstrates its capability to operate in the aqueous media with the detectable range of refractive indices of 1.33–1.36. A self-assembled monolayer (SAM) of long chain thiol is introduced to cover the surface of silver in order to prevent silver from deterioration. Experimental studies demonstrate that in this way, the sensor lifetime increases from days to weeks. This work provides a base for developing an affinity biosensor.

Detection of chemical vapours with a specifically coated optical-fibre sensor

Abstract In this paper, an intrinsic optical-fibre sensor is described. Continuous measurements of volatile organic compounds in dehydrated air are presented. This sensor is based on the absorption of the species to be detected in the polymeric cladding, which leads to a variation of the light power transmitted through the fibre. The principles of the chemical sensor are given, with an example of detection achieved with a sensitive optical cladding. The advantages of the heteropolysiloxane polymers as sensitive claddings are discussed. The chemical selectivity of the sensor is changed by incorporating different functions (amino, vinyl, glycidoxypropyl) in the heteropolysiloxane cladding. Different chemical vapours, such as water, ethanol, acetone, dichloromethane and aromatic compounds, have been detected with this device.

A simple intrinsic optical-fibre chemical sensor

Abstract This paper describes an intrinsic optical-fibre sensor for the measurement of variations of the refractive index of a medium acting as the cladding. A multimode fibre is illuminated with a laser beam incident at an oblique angle so that some of the rays trapped in the core are refracted if the index of the cladding is slightly shifted. Owing to the stability of the light source, a variation of about 2 × 10 −5 in the refractive index is readily detectable. The sensitivity and the linearity of the sensor depend on the angle of incidence of the collimated beam. This set-up can be used for the remote analysis of liquid or polymeric mixtures. The realization of a gas sensor is also presented: the bare core of the fibre is coated with a polymeric film whose refractive index varies during gas absorption. An example of methane detection at concentrations less than the lower explosive limit with a polyoxyethylene film is given. This simple and low-cost sensor can be used for detection of other gases after the preparation of specific sensitive claddings.

Chemical vapour sensing by surface plasmon resonance optical fibre sensor coated with fluoropolymer

Abstract A surface plasmon resonance fibre optic sensor has been developed allowing sensitive remote detection. A 50 nm thick silver film is deposited by thermal evaporation onto the silica core of the optical fibre. To protect silver from oxidation, self-assembled monolayers (SAM) of long-chain alkanethiols were used. For detecting gas and vapours, the surrounding dielectric medium consists of a polymeric material deposited on the modified metallic film. Chlorinated and aromatic compounds have been tested with detection limits of 0.3%, 0.7%, 1% and 2% for trichloroethylene, carbon tetrachloride, chloroform and methylene chloride, respectively, and 0.13%, 0.19% and 0.95% for xylene, toluene and benzene, respectively. For aromatic compounds, the response of the sensor depends on the boiling temperature, whereas for chlorinated compounds it depends on the difference between the refractive index of the analyte and specific polymeric cladding. Moreover, both the response time (about 2 min) and the desorption time (about 2.5 min) have been obtained with good reproducibility.

A simple intrinsic optical fibre refractometer

A refractometer using low-cost components is described. A multimode optical fibre is illuminated by a collimated beam at a variable oblique incidence angle. The value of the refractive index of a liquid is deduced from the measurement of an angle and does not depend on fluctuations of the light intensity. The use of an optical fibre allows remote sensing to be performed. As predicted by a simple theoretical analysis based on geometrical optics, the accuracy of the refractometer is about 1 × 10−4 in refractive index units. Owing to its good sensitivity, this set-up can be used as a chemical sensor.

Study of self-assembled monolayers of n-alkanethiol on a surface plasmon resonance fibre optic sensor

Abstract Surface plasmon resonance (SPR) is a powerful technique for direct sensitive (bio) chemical detection. This phenomenon can be used to measure the refractive index of either bulk chemical samples or chemically sensing thin layers. In this work, a surface plasmon resonance fibre optic sensor has been developed. A 50 nm thick silver film is deposited by thermal evaporation onto the silica core of the optical fibre. To protect silver from oxidation, the evaporated silver film was covered with self-assembled monolayers (SAMs) of long-chain alkanethiols (1-octadecanethiol). To characterize these SAMs, silver films evaporated onto macroscopic glass surface as test samples and several techniques such as contact-angle measurements (sessile drop method), X-ray photoelectron spectroscopy, and atomic force microscopy were used. Such a modified surface showed a high contact angle with water which remains stable after a one month stay in aqueous media. Similarly, a SPR fibre optic sensor showed no ageing problem, when kept in the same conditions.