Dominique Persegol

Modeling ion exchange in glass with concentration-dependent diffusion coefficients and mobilities

Multimode buried waveguides made in silicate glass by field- assisted ion exchange present very asymmetric profiles. We show how this phenomenon originates in the large dependence of the kinetics on the local ion concentrations. For this purpose, we derive an interdiffusion equation that includes the effects of concentration-dependent diffusion coefficients and mobilities. We show how to deduce this dependence from measurements on ion-diffused samples. The maximum concentra- tion of the incoming ions is computed from surface equilibrium conditions and is used in the interdiffusion equation as a limiting parameter for coefficient variations. To control the model accuracy for surface as well as buried waveguides, we measure ion profiles with three independent methods: M-lines, scanning electron microscopy, and near-field refrac- tometry. When applied to Ag 1 -Na 1 exchange in silicate glass, the model yields theoretical estimations in good agreement with experiments. This approach underlines the fundamentally nonlinear process that takes place during ion exchange and is also valuable to properly model single- mode waveguide fabrication.

Thermal diagnosis of medium-voltage switchboard: a cost-effective solution based on a multipoint optical sensor

We have developed an optical temperature sensor aimed at early detecting faults in Medium Voltage substations. The advantage of the sensor lies in its full suitability for the target application, which allows it to reach a cost compatible with the service rendered. Heavily doped ruby has shown to be attractive (fluorescence efficiency, cost) but also revealed a multi-fluorescence lifetime behavior. Accuracy of +/- 2 degree(s)C has been achieved over the -20 degree(s)C/+120 degree(s)C range for a 12 point sensor. We hope this system opens up interesting prospects in the field of thermal diagnosis, beyond its application in electric power industry.

Integrated optics interferometer for high precision displacement measurement

We present the design and fabrication aspects of an integrated optics interferometer used in the optical head of a compact and lightweight displacement sensor developed for spatial applications. The process for fabricating the waveguides of the optical chip is a double thermal ion exchange of silver and sodium in a silicate glass. This two step process is adapted for the fabrication of high numerical aperture buried waveguides having negligible losses for bending radius as low as 10 mm. The optical head of the sensor is composed of a reference arm, a sensing arm and an interferometer which generates a one dimensional fringe pattern allowing a multiphase detection. Four waveguides placed at the output of the interferometer deliver four ideally 90° phase shifted signals.

Spectral behavior of integrated optics asymmetric y-junction used for optimizing a planar optics telescope beam combiner

Astronomical aperture synthesis requires to combine beams coming from telescopes, with constraints on mechanical and thermal stability, accuracy on the measurement of the interferences visibility. One adapted way for solving the problem is integrated planar optics. A first two telescope beam combiner made by ion exchange technique on glass substrate and build with symmetric Y-junction provides laboratory white light interferograms simultaneously with photometric calibration. In order to increase the interferometric signal without loss of photometric output, we propose to replace symmetric Y-junctions by asymmetric ones. In this paper, we report the conception, the manufacturing and the characterization of asymmetric Y-junction realized by ion exchange on glass substrate. The specific application of astronomical interferometry required the characterization of such component in term of spectral behavior, so we report the simulation and the measurement of asymmetric Y-junction response versus wavelength.

Model of selectively buried optical waveguides

Selective buried waveguides have different regions, lying at various depths under the glass surface. This structure is formed by field-assisted inter-diffusion in an electrically inhomogeneous glass, with an electrical conductivity varying both spatially and in time. We present a simple, preliminary model of such a complex, two-dimensional structure. We explain the assumptions used to obtain a tractable model and discuss them in detail. Our results are illustrated by mono- mode structures, buried under normal electric field intensities. They are in qualitative agreement with experimental measurements. We discuss the improvements of the model, necessary to take into account spatial and temporal variations of glass properties.