Abstract
(English)
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The aim of the project is to exploit fully the technological potential of quantum cascade lasers and open the way to entirely new mid-infrared applications, conceivable only if implemented with high performance mid-ir semiconductor sources. Quantum cascade lasers, based on intraband transitions, form a new class of devices, which are revolutionizing the world of mid-infrared sources. To date, QC lasers are already functioning in pulsed operation at room temperature and above, over a very broad spectral range (5-12 µm). Single frequency QC-DFB lasers are available. However, the maximum operating temperature for continuous wave operation is still ~ 150 K, imposing a strong technological limitation for all systems which require high frequency modulation and/or narrow line width. We propose to develop and fabricate QC lasers operating in continuous wave mode on thermoelectric cooling elements, which meet the requirements of compact systems and could become the essential device for a new technology based on mid-infrared radiation.
Objectives:
Improved atmospheric telecommunications: Mid-infrared wavelengths are much less sensitive to scattering centres in the atmosphere such as fog, smog and dust particles. This insensitivity will allow the replacement of microwave RF links by mid-infrared systems which are smaller, exhibit directional gain and can easily be focused.
Large volume device production for narrow-band spectroscopy: Pulsed QC-DFB lasers are limited in linewidth. Continuous wave operation is therefore required. Cooling with closed-cycle cryocoolers is not feasible because of cost, volume, maintenance and energy requirements.
Work description:
In the present project we plan to address the major challenge of developing advanced optoelectronic and photonic devices, semiconductor light sources for mid-infrared applications (range: 4-15 µm). Our aim is to lay down the foundations of a new technology, which can radically reform the available sources of infrared radiation by developing semiconductor lasers that are compact, efficient, robust and highly manufacturable. To achieve our objectives the scientific investigation will be divided into the following 6 fields of research.
1) Design of active regions, waveguide design and new solutions for low loss optical confinement (re-growth); conception of small area devices by selective etching, ion implantation and lateral oxidation; high reflectivity concepts (coatings, Bragg reflectors, photonic band gap structures).
2) Growth novel QC structures and will be mostly carried out by the university partners. During the third year of the project Thomson will participate in the growth of GaAs structures and Alpes Lasers in the growth of InP structures - to assure the transfer of know-how from university to industry. InP re-growth will be achieved by exploiting the existing expertise at Thomson.
3) Processing: Ridge structures for testing of devices; disk-like resonators (low threshold currents); mushroom-like ridge waveguides, with ultra narrow current; double-trench planar technology for junction-down mounting; ion implantation for planar technology of gain guided devices.
4) High reflectivity mirrors: distributed Bragg gratings for low threshold QCLs;
High reflection coating of AlGaAs/GaAs QCLs; fabrication of two-dimensional photonic bandgap structures in QCLs; small area devices (ultra low currents) and specially shaped mirrors (using focused ion beam processing).
5) Characterization: integral and spectral light output of specially shaped resonators and mirrors; waveguide loss measurements in QCLs by a combination of multisectioned laser techniques and Fabry-Perot resonator Q measurements; rf modulation of Quantum Cascade lasers; reliability.
6) Mounting/Packaging: thermal design: packages allowing the operation of QCLs in continuous wave mode on a Peltier element; encapsulation.
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