Miroir A Réseau SUb-longueur d'onde Pour les LAsers à émission verticale dans le Moyen Infrarouge – MARSUPILAMI

Vertical cavity surface emitting lasers (VCSEL) have already demonstrated their excellent ability as compact sources for molecular spectroscopic measurements. For these applications, the mid-IR wavelengths (' > 2.6 µm) represent a major field of investigations since they allow the detection of molecules in various domains as different as environment (polluting gas detection,...), medicine (illness diagnostics, ...), food market or industrial process control (gas emission during process, security, ...), to cite few of them. A general issue for the long wavelength VCSELs is the inherent thick epitaxial structure (t=16µm for '=2.7 µm) leading to detrimental electro-thermo-optical properties. In addition for ' > 2 µm, new emerging materials such as the antimonide allloys system still suffer from lower efficiency of radiative recombination compared to conventional GaAs and InP. Nevertheless, excellent results have been recently demonstrated near 2.3 µm with Sb-materials. Even if InP-based technology permits highly performant electrically pumped (EP) VCSELs up to 2.3 µm, emission beyond 2.6 µm can only be realized with GaSb-based active layers. To encompass these difficulties, VCSEL emitting above 2µm have been demonstrated with hybrid dielectric-semiconductor structure. The monolithic solution should improve room temperature device performances for the aimed spectroscopic sensing applications. The ideal source would have sufficient optical power to ensure high signal-to-noise ratios; narrow linewidth to obtain high selectivity and sensitivity; single longitudinal mode operation for high selectivity and elimination of intermode competition noise; high beam quality, i.e., small beam divergence; rapid wavelength tunability for fast response and high data acquisition rates; and minimal susceptibility to changing environmental conditions. VCSELs exhibit the majority of these properties but the polarization control and the single-mode operation remains problematic. In this project, we propose to develop a sub-wavelength grating mirror, to be integrated within a Sb-based VCSEL emitting beyond 2.6 µm. In addition to solve the problems related to the laser structure thickness, such a mirror would allow to control through its design the polarization of the emitted light while contributing to sustainable transverse single-mode operation. The simulation and the design of this mirror would be ensured thanks to an original method of calculation based on cellular automata. Moreover, the development of this mirror implies technological targets as the etching control of antimonide alloys on a nanometric scale, but also the wet oxidation of these alloys. Our project proposal thus address an experimental development of EP-mid-IR-VCSELs, aiming for a extension of the emission wavelength above 2.5µm together with a significant improvement of their electro-optical performances.