Advanced optical components for mid-infrared applications

The mid-infrared wavelength range, defined from 2.5 um to 25 um is of a high scientific and technological interest. One of its main application field is in spectroscopy, since these wavelengths coincidewith the fundamental rotational-vibrational modes of many molecules. While the typical optical sensing setup is composed of active elements - detectors and radiation sources- it also requires critical passive components such as lenses, filters and an interface with the medium to be probed. To this day, most of the scientific work in mid-infrared has been mostly focused on active elements such as the quantum cascade laser. While very modern detectors and lasers are now available, the experimental setups still rely on classical and bulky passive optics. The work presented in this thesis explores modern optical technologies for the realization of novel passive mid-infrared optical components. The fabrication of an external cavity tunable quantum cascade laser emitting from 7.6 um to 8.1 um is presented. This thesis describes the fundamentals of sub-wavelength structures for optical phase generation. Such structures allow local modifications of the effective refractive index of a dielectric material. Using these concepts, original designs of polarizers, anti-reflective and diffractive micro-optical elements are proposed for high-index dielectrics such as silicon or germanium. In particular, the fabrication and characterization of a novel binary grating in silicon that combines anti-reflective and diffractive functions around 7.85 um is presented. This component is characterized using the developed tunable light source setup. Another type of optical component is presented, based one dimensional photonic crystals. It consists of a ZnSe-YbF3 multi-layer deposited on top of a CaF2 substrate. This element allows to observe the first occurrence of Bloch surface waves in the mid-infrared, using the same tunable laser setup. The evanescent field of a surface-propagating wave can be used to probe the surrounding medium. Such structures are promising novel types of substrates for surface-based sensing applications. In addition, a quantum cascade laser-based setup for the detection of cocaine in liquid is presented. This experiment illustrates the great potential of quantum cascade lasers for compact chemical sensing setups.