【海韵讲座第27场】

时间：2012年11月20日周二 上午9：00

地点：海韵园行政楼C505报告厅

VCSEL based light sources - Challenges for application in Exascale Computing, Computer Farms and Green Photonics

By Prof. Dr. Werner Hofmann (Technical University of Berlin)

讲座摘要

The copper-induced communication bottleneck is inhibiting performance and environmental acceptance of today´s supercomputers. Vertical-cavity surface-emitting lasers (VCSELs) are ideally suited to solve this dilemma. Indeed global players like Google, Intel, HP orIBM are now going for optical interconnects based on VCSELs. Future high-performance computers require optical interconnects with aggregated Exa-Byte/s data transport. Densely packed arrays of vertical-cavity surface-emitting lasers (VCSELs) might present the only feasible technical solution. The high-speed properties of semiconductor lasers, however, are strongly affected by their operating temperature. Thermal crosstalk becomes dominant when densely packed arrays of high-speed VCSELs are required. Having these applications in mind, we recently realized ultra-high speed VCSELs suited for optical interconnects in data centers with record-high performance. The 980-nm wavelength was chosen to be able to realize densely-packed, bottom-emitting devices particularly advantageous for interconnects. These devices show error-free transmission at temperatures up to 155°C. Serial data-rates of 40 Gb/s were achieved up to 75°C. Peltier-cooled devices were modulated up to 50 Gb/s. The novel VCSELs feature a new active region, a very short laser cavity, and a drastically improved thermal resistance by the incorporation of a binary bottom mirror. All device data were measured, mapped and evaluated by our fully automated probe station. These device results deliver the basis of projections of future systems. The maximum bandwidth of future VCSEL-based optical interconnects can be derived from the influence of device heating occurring in high-speed VCSEL arrays. Furthermore, the scalability of this technology and its challenges are addressed. From calculations we obtain, that VCSEL arrays are scalable from a bandwidth density of 100 Gbps/mm² with today´s devices up to a technological limit of 15 Tbps/mm².

讲座人简介

Werner Hofmann was born in Erlenbach, Germany, in 1978. He received his Dipl. Ing. (M.S.) degree in electrical engineering and information technology (IT) in 2003 the Dr. Ing. (PhD) degree in 2009, both from the Technical University of Munich, Germany. From 2003 to 2008 he has been with the Walter Schottky Institute where he was engaged in research on InP-based vertical-cavity surface-emitting lasers (VCSELs). This work was done within a very successfully in collaboration with the group of Prof. Zhu Ninghua, Institute of Semiconductors, CAS, Beijing. He then joined Prof. Connie Chang-Hasnain´s group at the University of California, Berkeley. At UCB he worked on the incorporation of high-contrast gratings (HCG) into long-wavelength VCSEL devices. In 2010 he joined the group of Prof. Dieter Bimberg at the Institute of Solid State Physics at the Technical University of Berlin, Germany as principal scientist (associate professor equivalent) focusing his work on GaAs-based ultra-high-speed surface emitters. Concurrently, he is a CTO of the Center of Nanophotonics at TU Berlin. In 2012 he was offered a full professorship (W1-level) in nanophotonics at TU Berlin. He has authored or co-authored some 100 articles (including several invited) in scientific journals, conference proceedings and books. He is a recipient of the E.ON Future Award 2009, one of the most highly endowed research awards sponsored by the German Industry. Dr. Hofmann is a member of the Association of German Engineers (VDI), and a member of the IEEE Photonics Society.