Optical fibers and microstructured optical fibers
Contact : Johann Trolès
The glasses and ceramics group has developed a drawing tower specially designed for drawing soft glass fibers until 900-1000°C and more particularly designed for drawing chalcogenide fibers. Single index fibers, step index fibers and microstructured optical fibers are examples of optical fibers that can be prepared and studied in our lab. In addition, before drawing, high optical quality glasses have to be obtained. In this context, important researches are devoted to the purification of the raw materials and the glasses. Those studies are essential in order to obtained high transmission optical fibers.
Contact : Odile Merdrignac
Transparent polycrystalline ceramics are an emerging class of optical materials that can reproduce the optical properties of single crystals and glasses while offering enhanced thermomechanical properties. The development of ceramics transparent in the infrared is of great interest to the civil and military sectors, for example, for thermal imaging and the manufacture of missile domes. Zinc sulfide (ZnS), the dome material currently in use, is produced by CVD and HIP techniques as coarse-grained ceramics with low hardness which do not satisfactorily meet the erosion resistance requirement. The Glass and Ceramics group has developed a sintering process using nanopowders (patented) to produce transparent ZnS ceramics of comparable optical quality and twice the hardness of commercial products. The innovative process also makes it possible to significantly reduce the cost of optics, suggesting a democratization of applications, particularly for the civilian field.
The expertise acquired in the manufacture of ZnS optics has led to real advances in the ability to create new materials that are transparent in the infrared. Cubic ternary sulfides, like calcium lanthanum sulfide (CaLa2S4), are currently under investigation in the framework of ANR project and PhD studies.
Main collaborations: DGA, Solcera Advanced Materials (Evreux)
We have also shown the very high efficiency of ZnS and CaLa2S4 powders as host matrices, respectively, of transition metal and rare earths ions, for the emission in the mid-infrared and the conversion of frequency. By capitalizing on the expertise acquired in the manufacture of transparent ceramics, we can expect the generation of new light sources in the mid-IR (3-5μm) and new solid-state laser gain media.
Thin film and waveguides
New Generation of mid-IR sources
One of the main challenges of this research activity is to study and to develop IR fibre lasers emitting beyond 3 µm. Two ways are investigated: luminescence of rare earth and supercontinuum generation. A Supercontinuum generation consists in a spectral broadening of a light pulse by using strong nonlinear effects. It can be noted that currently the commercial IR spectrometers use classical black body sources which are not coherent as regards light or powerful light. With the developed fibre laser, we can expect a light power 100 to 1000 as high as the light emission of a black body. In the case of a fibre laser, all of the light is concentrated in the core of the fibre that can be smaller than 10 µm diameter which enables to obtain a light/surface ratio never observed in the mid-IR.
The main infrared signatures of molecular compounds are included in the transparency windows of the chalcogenide fibers and waveguides. Thus, optical fibres or waveguides can be practical sensing tools. Indeed, they transport light to and from the sensing region. In such configurations, the interaction between the light and the environment occurs at the surface of the fibre. The vibrational spectrum which is collected at the output of the fibre constitutes an IR signature very specific of the chemical or biological species. They are consequently good candidates to be used in biological/chemical sensing. In this respect, in the past decade, chalcogenide glass fibres and waveguides have been successfully implemented in Mid-IR spectroscopy experiments, for the detection of bio-chemical species in various fields of applications including water pollution, microbiology and medicine and CO2 detection.