Optical Interconnect Technologies based on Silicon Photonics
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Optical Interconnect Technologies based on Silicon Photonics Wim Bogaerts1, Philippe Absil2, Dries Van Thourhout1, Joris Van Campenhout2, Shankar Kumar Selvaraja1, Pieter Dumon1, Hui Yu1, Adil Masood1, Gunther Roelkens1, Roel Baets1 1
Ghent University – imec, Department of Information Technology, Photonics Research Group, Sint-Pietersnieuwstraat 41 9000 Gent, Belgium
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imec Belgium, Kapeldreef 75 3001 Leuven, Belgium
ABSTRACT We discuss the principles of Optical interconnects, and discuss the potential of silicon photonics to provide all the necessary building blocks to construct dense, high-bandwidth, lowpower optical links. We discuss waveguides, wavelength division multiplexing, modulators and photodetectors. We also take a look at the options for implementing light sources, a function which silicon cannot natively provide, with a focus on implementations in the IMEC silicon photonics platform. INTRODUCTION Optical communication is not new. The laser diode and the optical fiber have sparked a dramatic breakthrough for long-distance telecommunication. Optical fibers supported larger bandwidths over a long distance. Thus, optical links quickly became the backbone of the internet. Given the fact that is most communication systems people start from an installed base and gradually expand it, it is clear that electrical communication is prevalent inside the closed 'box', while optical links are easier to connect boxes together. The notion of a box depends on the application, but in general the physical dimension of the box is shrinking. 40 years ago, optical links connected continents, but since then optical interconnects have penetrated metropolitan networks (box = town), access networks (box = building) and supercomputing infrastructure (box = rack). This expansion has been accompanied with a reduction in cost, size and power consumption of the photonic components in the optical link. More recently, optical links are being considered for board-to-board interconnects and even on-chip interconnects, where cores and memory could be considered as yet another set of boxes [1] While light is just another form of electromagnetic radiation, its base frequency is in the order of several hundreds of THz: it can be used like a frequency carrier for a signal with lower bandwidth, which could still cover tens of THz. Also, optical fibers have extremely low propagation losses, allowing point-to-point links of over 100km. This gives optical communication a huge bandwidth×distance product. Also, the optical signals will not radiate and cause no electromagnetic interference and crosstalk.
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While the bandwidth for optical signals is tens of THz, its use is limited by the electrical modulation and detection of the signals. Therefore, most telecom links adopt Wavelength Division Multiplexing (WDM): signals are encoded onto different carrier wavelengths, which are transmitted independently through the same physical channel, not unlike FM and TV channels share the same medium (air or cable). In WDM, the carriers are typically gen
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