Abstract: 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 or IBM 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. a self-consistent approach based on the Boltzmann transport equation in the high field regime within the device geometries, and boundary conditions. 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.
Biography：Dr. Werner Hofmann was born in Erlenbach, Germany, in 1978. He received the Dopl. –Tng. (M.S.) degree in electrical engineering and information technology and Dr. –Ing. Degree from the Technical University of Munich (Technische Universitat Munchen), Munich, Germany, in 2003 and 2009, respectively.In 2003, he was with the Walt Schottky Institute, Technical University of Munich, where he was engaged in research on InP-based vertical-cavity surface-emitting lasers (VCSELs) including design, manufacturing and characterization. In 2009, he joined the University of California, Berkeley, via a Postdoctoral Fellowship Program granted by DAAD (German Academic Exchange Service). He is the author or coauthor of more than 60 articles (including several invited) in scientific journals, conference proceedings and books on long-wave-length VCSELs and their applications.Dr. Hofmann is a member of the Association of German Engineers (VDI) and the IEEE Photonics Society.