Nouvelles sources lasers massivement accordables pour les applications télécom et les nouveaux capteurs

摘要

This thesis focuses on the study and realization of broadband vertical cavity lasers emitting at 1,55 µm, useful for telecom applications, integrated sensors and medical imaging. ln order to achieve tunable VCSELs over broad spectral range( 50 nm), this thesis focused on the study and improvement the key components of these devices, which are: Bragg mirrors, active region and optical and thermal performances of VCSELs. The high index contrast (Δn~1,9) of dielectric materials (a-Si/a-SiN.) allowed a large bandwidth mirror (~700 nm) and high reflectivity (99.6%), ensuring a good VCSEL operation. For the active region, we opted for using quantum dashes, and thanks to their size dispersion allow having a broadband gain material. The realization of the quantum dashes based VCSEL with dielectric mirrors allowed a first international demonstration of a laser emission over a broadband of 117 nm, covering the optical telecommunication C and L bands. The laser emission is obtained under continuous optical pumping up to 42°C with a maximum output power of 1.3 mW. To improve the emitted laser power, a study based on the number of the output mirror pairs was conducted. For a variable number of pairs (4, 5 and 6 pairs), the best compromise was obtained for an output mirror with 4 pairs only, for which the output power is increasing from 0.1 mW (6 pairs) to 1.3 mW (4 pairs). ln this case, besides the increase of the output power, performance improvement is also reflected by improved external differential quantum efficiency of the laser and an increase in the operating range of the pump power. To improve the thermal aspect of the VCSEL, an approach based on the use of hybrid mirror was developed. This allows to keep even to improve the reflectivity of the standard dielectric mirror while reducing its number of pairs. Experimentally, it has been demonstrated a 29 % reduction in thermal resistance, confirming the effectiveness of the hybrid mirror to be a potential alternative to standard dielectric mirror. This improvement in term of thermal dissipation allowed an increase in operating temperature up to 45°C and a maximum output power of 1.8 mW. The realization of TSHEC process based on buried hybrid mirror, allowed further optical and thermal enhancements. Thus, with a 20 µm Bragg mirror diameter, we have demonstrated a maximum output power of 2.2 mW with a larger pump power operating range and a temperature operating up to 55 °C. All these optimizations will soon be implemented within the tunable VCSEL structures of HYPOCAMP ANR project.