In April 2008 the European project SUBTUNE (Widely Tuneable VCSELs using subwavelength gratings) started and will last for three years. This project aims to realize VCSELs (Vertical Cavity Surface Emitting Lasers) tuneable in wavelength over large intervals using different techniques, so to cover different emission windows and applications: 850nm, 1550nm and 2000nm. To that end the MEMS (Micro Electro Mechanical Systems, see Focus 2003) technology will be adopted to realize an optical cavity of variable length. This is achieved thanks to a top mirror separated from the half VCSEL by an air-gap and movable by electro-thermal or electrostatic actuation. Recently one of the partners of the consortium (TUD Darmstadt) has demonstrated a tuning range of 75nm in a device of 1550nm, which is a world record. To cover the different wavelength windows and the corresponding applications eight European partners concur to the project: : Technische Universitaet Darmstadt (TUD), Germany, Chalmers University of Technology, Sweden, Tyndall National Institute at University College Cork, Ireland, Technical University Munich (TUM), Germany, VERTILAS GmbH, Germany, IR-Microsystems (IRM), Switzerland, LIST Commissariat de l'Energie Atomique (CEA LIST), France, Consiglio Nazionale delle Ricerche IEIIT-CNR (scientific responsible Pierluigi Debernardi). The applications of such devices are variegated, from datacom (WDM at 850 and 1550nm) to sensing e environment monitoring (sensors or temperature, deformations, composition of gases).
The role of IEIIT is to design and optimize the devices. IEIIT has been chosen for its decennal experience in the 3D (three-dimensional) and vectorial simulation of VCSEL and for its skills in the simulations of VCSELs with dielectric gratings. In fact one of the main objectives of this project is to introduce in the structures a dielectric grating with the aim of fixing the emitted polarization of the light. This is in fact an essential property in the sensing applications and the unit IEIIT, together with Ulm university, has proposed and implemented successfully for the first time this technique to face a problem whose solution has been searched for more than a decade. Such technique is today used in production and by several research centres all over the world. The collaboration preceding the start of the project with the coordinating unit of SUBTUNE (TUD Darmstadt) carried out a good agreement between the electromagnetic model and the experimental results achieved in Darmstadt is reported.
During the first year of the project, novel designs of such devices have been made and the possibility of simulating curved gratings introduced into the computer code.
Focus