Non conventional optical systems

Dissolved methane optical sensor :

 Structure test du capteur de CH4 composée de guides optiques diffractifs juxtaposés (le pas des réseaux de diffraction est égal à 1,28 µm).
Test structure of the CH4 sensor made of side-by-side diffractive optical waveguides (grating pitch of 1.28µm).

Methane (CH4) is a recognized source of alternative energy and contributes to at least 20% of greenhouse gases. Oceans store considerable amounts of this gas and innovative sensors need to be developped to be able to study its geographic distribution. In collaboration with two other laboratories (GET Toulouse and ENS Lyon), we proposed an integrated optic sensor which, through a simple angular measurement, allows the detection of  time-varying minute concentrations of methane dissolved in sea water. The sensor exploits a diffractive optical waveguide coated with a methane-sensitive polymer layer. This device is designed to operate under high pressures and in high-temperature-gradient environments (P ~ 450 bars, T ~ 0 à 400°C) to meet the requirements of methane exploration near the ocean floor and more specifically close to hydrothermal sources.

Related publications :
  • Emerging technologies for in-situ dissolved methane measurements : S.AOUBA, C.BOULART, O.CARRAZ, P.ARGUEL, M.AUFRAY, P.BEHRA, O.BERNAL, A.CASTILLO, M.CATTOEN, V.CHAVAGNAC, B.DUBREUIL, J.P.DUTASTA, F.LOZES-DUPUY, P.GISQUET, HC.SEAT, Environmental Sensors 2012 du 23 septembre au 28 septembre 2012, Anglet (France), Septembre 2012, 1p. (Résumé) , N° 12843
  • Deep sea observatory: a need of in situ dissolved methane sensor : V.CHAVAGNAC, C.BOULART, O.CARRAZ, HC.SEAT, M.CATTOEN, T.BOSCH, S.AOUBA, P.ARGUEL, F.LOZES-DUPUY, B.DUBREUIL, M.AUFRAY, P.BEHRA, Workshop MAISOE - RTRA - STAE 2011 du 21 novembre au 23 novembre 2011, Aspet (France), Novembre 2011, 1p. (Résumé) , N° 11882 

Silicon-based monolithic micro-interferometer :

Représentation schématique du micro-interféromètre intégrant un réseau d'amplitude et une photodiode. (Encadré : Photographie du dispositif opérationnel constitué d'une photodiode recouverte d'un réseau de période égale à 1 µm.)
Schematic drawing of the micro-interferometer made of a grating and a photodiode. (Insert : Picture of a fully-operational device constituted of a 1µm-pitch grating integrated on top of a photodiode).

Integrating both optical and electronic functionalities on a single chip enables the fabrication of compact and robust systems which, in turn, open new opportunities or applications. In this context, we have experimentally demonstrated a micro-interferometer which monolithically integrates the beam-combining and photo-detection functions and which can be made using standard CMOS technology. The device enables the measurement of free-space optical phase difference, a parameter used in many sensing applications such as thermal expansion, concentration, pressure or displacement sensing and monitoring. It also paves the way towards the development of innovative equipments including optical data storage, 3-dimensional imaging, digital holography, or wavefront analysis systems. Finally, using a judiciously designed array, the amplitude, phase and polarisation content of a free-space-propagating optical beam could be simultaneously measured.

Related publications :

Polarization independent guided mode resonant filters (GMRFs):

Cartographie du coefficient de réflexion du filtre pour tous les états de polarisation incidente (au voisinage de la longueur d'onde de 1580 nm).
2D map of the reflection coefficient of polarization independent GMRF as a function of both wavelength and polariztion state of the incident beam (angle of incidence 12°).

To address the ever increasing requirements of sattelite observation and, in collaboration with CNES (Toulouse) and the Institut Fresnel (Marseille), we investigate a novel generation of wavelength-tunable high-spectral-selectivity and polarisation-independent filters. An innovative filter which combines two waveguides and two crossed 1D gratings has been proposed and experimentally demonstrated. In the near infrared and under oblique incidence, such reflective filter has been shown to provide a reflection with widely tunable (> 100 nm) central wavelength, narrow (1nm , quality factor of 2300) bandwidth and (within 3%) polarisation-independent response. This study is being furthered as a dedicated collaborative research project with CNES.

Related publications :