In short-range interconnect applications, one question arises frequently: When should optical solutions be chosen over
electrical wiring? The answer to this question of course depends on several factors like costs, performance, reliability,
availability of testing equipment and knowledge about optical technologies, and last but not least, it strongly depends on
the application itself. Networking in high performance computing (HPC) is one such example. With bit rates around 10
Gbit/s per channel and cable length above 2 m, the high attenuation of electrical cables leads to a clear preference of
optical or active optical cables (AOC) for most planned HPC systems. For AOCs, the electro-optical conversion is
realized inside the connector housing, while for purely optical cables, the conversion is done at the edge of the board.
Proceeding to 25 Gbit/s and higher, attenuation and loss of signal quality become critical. Therefore, either significantly
more effort has to be spent on the electrical side, or the package for conversion has to be integrated closer to the chip,
thus requiring new packaging technologies. The paper provides a state of the art overview of packaging concepts for
short range interconnects, it describes the main challenges of optical package integration and illustrates new concepts
and trends in this research area.
Evolution in high performance computing (HPC) leads to increasing demands on bandwidth, connectivity and flexibility.
Active optical cables (AOC) are of special interest, combining the benefits of electrical connectors and optical
transmission. Optimization and development of AOC solutions requires enhancements concerning different technology
barriers. Area and volume occupied by connectors is of special interest within HPC networks. This led to the
development of a 12x AOC for the mini-HT connector creating the densest AOC available. In order to integrate
electrical optical conversion into a module not higher than 3 mm, a new concept of coupling fibers to VCSELs or
photodiodes had to be developed. This unique concept is based on a direct replication process of an integrated fiber
coupler consisting of a 90° light deflecting and focusing mirror, a fiber guiding structure, and a fiber funnel. The
integrated fiber coupler is directly replicated on top of active components, reducing the distance between active
components and fibers to a minimum, thus providing a highly efficient light coupling. As AOC prototype, multi-chipmodules
(MCM) including the complete electrical to optical conversion for send and receive connected by two 12x fiber
ribbons have been developed. The paper presents the integrated fiber coupling technique and also design and
measurement data of the prototype.