news review
40 Gbit/s VCSELs combine speed and reliability RESEARCHERS working on the European Commission funded Vertically Integrated Systems for Information Transfer (VISIT) programme have demonstrated high reliability Vertical Cavity Surface Emitting Laser (VCSEL) devices operating at data rates of up to 40 Gbit/s.
VISIT is an EU funded programme with the remit to focus on strategic, high-value photonic components and subsystems for scalable economic broadband access and local area networks.
The central objective of the VISIT programme, which started in October 2008, is the research, development, test and exploitation of system-enabling optical transmitters having a completely novel design and/or largely improved functionality as compared to current technology.
The directly modulated VCSEL devices, fabricated on material grown by IQE at its Cardiff facility, operate at 850nm, which is the current standard wavelength for optical fibre applications used in short-reach data communication and storage area networks.
The new technology increases data throughput by up to 400 times the speed of current copper Ethernet systems and four times that of the latest optical technologies. The VCSEL devices also demonstrated superb temperature stability
in the linear region of the light power versus current characteristic with a less than 25 µW/oC change in emission power for operation below 6 mA at temperatures between 20 to 100oC.
The peak output power exceeded 8 mW for multi-mode operation and up to 4 mW for single mode operation, all with differential slope efficiencies exceeding 70% at up to 40oC.
Multi-mode VCSEL device operation was demonstrated at current densities well below 10 kA/cm2, which is a critical factor in determining device reliability. This is expected to greatly improve with the further development of single-mode VCSELs. The VISIT team has also produced the first 40 Gbit/s packaged VCSELs, complete with an OM3 fibre pigtail and a high frequency electrical V- connector for ease of system-level optical link testing and development.
The prototype VCSEL devices fabricated using new device processing techniques and device geometries on wafers produced by IQE’s optoelectronic facility in Cardiff, UK, operated reliably at 40 Gbit/s in initial tests, making them suitable for optical interconnectors as well as for optical fibre networks for high data rate applications such as data centres.
The next development stage under the VISIT programme will focus on final directly modulated VCSEL benchmarking and design and processing refinement including device designs for reliability and manufacturability. The VISIT team will also work on further improvements in the packaging and testing of optical transmitter subassemblies.
The VISIT Project is funded by the European Commission Framework 7 Programme with Project Officer Michael Hohenbichler.
The project is led by Dieter Bimberg of the Technical University of Berlin (Germany), and includes also the following project partners: IQE (UK), Intel, (Ireland), VI Systems GmbH (Germany), Chalmers University of Technology (Sweden), The University of Cambridge (UK), University College Cork via the Tyndall National Institute (Ireland), Riber S.A. (France) and the A.F. Ioffe Physical- Technical Institute of the Russian Academy of Sciences (Russia).
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www.compoundsemiconductor.net November/December 2011
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