Optical communications

This research line covers five research topics:

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Integrated Optics and semiconductor lasers

The research group has a broad experience in integrated optics in collaboration with INTEC of university of Ghent (Belgium). We also collaborate with Brussels University, Belgium (Dr. Krassimir Panajotov), in the design and fabrication of semiconductor lasers, such as the new VCSELs using short external cavities. Part of the design and characterization of both kind of devices has been carried out in our facilities.

This research line has been devoted to the development of new low-loss leaky structures. The typical refractive index difference in a III--V semiconductor waveguide is generally larger than 0.1, leading to mode sizes smaller than 2 micrometers. Besides, due to the planar technology used in the fabrication of semiconductor waveguides, the mode shape is highly asymmetric. The very small refractive index difference in a single mode glass fiber or silica waveguide (< 5x10-3) results in a weakly guided circular mode with a typical mode size of 8-10 micrometers. Direct butt-coupling between an optoelectronic device and a silica fiber or waveguide causes tipically 7-10 dB loss.

We have investigated new low-loss leaky structures and applied then in two new mode-expanded device. The resulting new spot size converters are very easy to fabricate and present good performance. The first one uses vertical anti-resonant reflecting optical waveguides (ARROW) as fiber (or silica waveguide) matched waveguides.We have investigated how to simplify the growing of the layers. The second spot-size converter applies leaky confinement for both vertical and lateral directions simplifying not only the growth of the device but also the processing, to the minimum fabrication steps needed for a standard waveguide: one growth and one etching step. The investigated devices are made in the InP/InGaAsP material system for emission at 1.55 micrometers.

Contact: Marko Galarza, Mikel Arizaleta