Evanescent wave optical micro-sensor based on chalcogenide glass

A micro-sensor based on chalcogenide glasses was developed on oxidized silicon substrate for evanescent wave detection in near-infrared spectral domain. This micro-sensor is composed of ridge waveguides based on chalcogenide glass deposited by RF magnetron sputtering associated with a microfluidic system. Optical losses of the ridge waveguide were measured at 1.55 μm and were about of 0.4 dB/cm, a value sufficiently low to enable detection in near-IR spectral range by evanescent waves. Suitability of the sensor for chemical-sensing has been demonstrated by detecting phenylethylamine molecules absorbing specifically at 1.55 μm. The efficiency of the optical sensor was tested as a function of the phenylethylamine concentration in the solution and as a function of the waveguide effective area. The best sensitivity was obtained for the waveguide presenting the smallest effective area of about 1 μm × 1 μm when the attenuation was nearly linear with the phenylethylamine concentration. Experimentally, the resolution was about 0.1 mol L−1 and the sensitivity was 0.87 dB/(mol L−1). A theoretical study was set-up to better control the evanescent wave sensor performance in terms of sensitivity and of resolution of the optical chalcogenide micro-sensor. Finally, selenide micro-waveguides were developed on CaF2 substrates suitable for detection in mid-IR spectral range.