LONDON VCSEL optoelectronic materials produced at IQE plc's Cardiff manufacturing facility have enabled researchers to produce potentially reliable devices capable of operating at speeds greatly in excess of 10 Gbit/s.
The project was supported by the European project VISIT and the Swedish Foundation for Strategic Research.
In an article published in Electronics Letters , Professor Anders Larsson of Sweden’s Chalmers University of Technology said, “The vertical cavity surface emitting laser (VCSEL) emitting at 850 nm has become the laser of choice for short reach data communication links in local and storage area networks operating at single channel data rates up to 10 Gbit/s. While there is a future need for even higher data rates it has been commonly believed that VCSELs operating at rates much higher than 10 Gbit/s will have to be scaled down in size to achieve the modulation bandwidth needed, thus operating at current densities too high for reliable operation.”
Professor Larsson’s research group at the Photonics Laboratory at the Department of Microtechnology and Nanoscience, Chalmers University of Technology, in Göteborg, Sweden, has recently shown that this is not necessarily the case. By optimizing the VCSEL design with respect to differential gain, capacitance, electrical resistance and thermal impedance, it was demonstrated that 850 nm oxide confined VCSELs with an aperture as large as 9 µm can achieve low threshold current, high differential efficiency and a modulation bandwidth as large as 21 GHz.
At a bias current of 6.5 mA, clear and open eyes could be generated at bit rates up to 25 Gbit/s and an extinction ratio of 6 dB. This current corresponds to a current density of 10 kA/cm2, which is at the level where the present 10 Gbit/s VCSEL technology operates. This clearly indicates the potential for reliable operation of directly modulated 850 nm VCSELs at very high data rates for future, high capacity data communication links.