Tuneable QCL

Designing a tuneable Quantum Cascade Laser for mid-infrared frequency operation

This project focuses on the development of new external cavity tunable laser sources in the mid-infrared (MIR, 3-12µm), using Quantum Cascade Lasers (QCLs) as the gain medium and using novel wavelength selective mirrors inspired from Guided Mode Reflective Filters (GMRF), the so-called Cavity Resonant Integrated Grating Filters (CRIGFs). The ultimate goal is the demonstration of MIR, tunable QCL systems in external cavity with unprecedented performances and robustness outranging the state of the art external cavities in the MIR.
CRIGF filters allow the realization of reflective filters of high reflectivity and narrow bandwidth, just like GMRF, but with an extremely high angular acceptance. This unique particularity in turn allows the realization of simplified cat’s eye like external cavity semiconductor lasers. The cavity is only made of three elements, the laser diode (LD) amplifier, a ball lens and the CRIGF filter, with an object/image relation between the filter and the emission facet. These external cavities elements are made highly tolerant and robust with respect to misalignment by the object/image relationship existing between the mirror and the LD facet, avoiding classical alignment problems found with current grating-tunable cavities using Littrow or Littman-Metcalf configurations.
Moreover, the use of CRIGF filter allows to independently design and adjust the different parameters of the external cavity setup: beam size, spectral selectivity and tuning slope can all be independently adjusted, therefore simplifying the cavity design.