CALITREC

The CALITREC 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. CALITREC will proceed in three phases to demonstrate tunable external cavity QCLs in two spectral regions. - The first phase will focus on MIR CRIGF design and demonstration. - In a second phase, the project will focus on the demonstration of EC-QCL using discrete CRIGF filters and continuously varying CRIGF filters, with a strong emphasis on spectral precision and tuning repeatability, are those appear to be two key points for EC-QCLs that can be improved by the use of CRIGF mirrors. - The last phase will focus on broadband tuning (class 100 cm-1) of CRIGF-EC-QCL coupled with narrow band mode hop free (MHF) tuning of such systems. The expected outputs of the project are numerous. On the practical side, we expect to demonstrate tunable cavity QCLs with state of the art performance and record tunability, in the two atmospheric spectral windows of the MIR, i.e. 3-5µm and 8-12µm, using generic technologies and concepts that will be easily transposable to any other wavelength within QCL reach. On the theoretical side, we will develop novel modelling tools to design and conceive finite size periodic structures. On the experimental side, we will develop a novel generation of QCL and CRIGF structures that will find potential application on a larger scale than the sole project. To achieve these goals, the CALITREC project gathers expertise of 4 groups with complementary experience. State of the art QCL technology and performance analysis is provided through the III-V lab with renowned expertise in this field, CRIGF modelling will be dealt with at Institut Fresnel where a large experience on the modelling of sub-wavelength gratings has been established. LAAS is the only French group with expertise on both CRIGF and their implementation in external cavity, and Ecole Centrale Paris with its experience in MIR spectroscopy will provide quantitative measurements of CRIGF reflectivity and physical insight into their working principles to validate the developed models.