The April issue of the premier scientific magazine Nature Photonics publishes
the first experimental proof of all-optical ultra-fast communication signal
processing with silicon-based devices for transmission speeds above 100Gbit/s.
The paper results from the collaboration between University of Karlsruhe, Germany;
IMEC, Leuven, Belgium; Lehigh
University, USA and ETH Zürich, Switzerland. The achievements are a key
step towards the development of complex silicon-based photonic integrated circuits.
All-optical signal processing is particularly of interest in telecommunications
applications, where speed, power and cost are crucial. A key element to enable
all-optical processing is optical waveguides with highly nonlinear and ultra-fast
performance. Researchers from University of Karlsruhe, IMEC and its associated
laboratory INTEC at Ghent University, Lehigh University and ETH Zürich
fabricated an innovative optical waveguide structure by combining deep-ultraviolet
lithography, standard CMOS processing and organic molecular beam deposition.
This so-called silicon-organic hybrid (SOH) approach enables the fabrication
of waveguides which pave the way towards all-optical processing, where photons
do no longer need to be converted to electrons. This is considered to be one
of the most promising ways to handle the rapidly increasing global communication
A 4mm long SOH waveguide with a record nonlinearity coefficient of ? ˜
105(Wkm)-1 in the 1.55µm telecommunication window proved the capability
of the SOH concept. As such, record values predicted by theory have for the
first time been experimentally confirmed. Based on these waveguides, all-optical
demultiplexing of a 170.8Gbit/s telecommunication signal to 42.7Gbit/s was performed
using four-wave mixing. This is the fastest silicon photonic optical signal
processing demonstrated to date. This experiment proved the viability of the
SOH waveguides for all-optical processing of broadband telecommunication signals.
With the SOH approach, some inherent limitations of silicon could be overcome.
Silicon-based technology, in particular silicon-on-insulator (SOI) technology,
has already proven very successful for the fabrication of various passive linear
optical devices such as filters. The development of ultra-fast active Si-based
functionalities, such as all-optical switching, remained challenging due to
the slow dynamics caused by unwanted non-linear effects in silicon. So far,
the data rate achieved by using bare silicon waveguides was limited to only
40Gbit/s. The SOH approach overcomes this intrinsic limitation - thus enabling
data rates above 100Gbit/s - by combining the best of two worlds: mature CMOS
processing is used to fabricate the waveguide, and organic molecular beam deposition
is used to cover it with organic molecules. These molecules efficiently transfer
all-optical interaction without introducing significant absorption. The ability
of the organic material to homogeneously fill the slot between the waveguides
is a key feature of the deposition process.
The silicon circuits were designed by researchers of the University of Karlsruhe
in a fabless way, and were fabricated through the ePIXfab service on IMEC's
200mm silicon photonics platform. ePIXfab (www.epixfab.eu) is a European funded
initiative coordinated by IMEC to allow cost-effective fabless prototyping in
wafer-scale silicon photonics technology for R&D. ePIXfab runs multi-project
wafer shuttles in which designs from world-wide users share mask and processing
IMEC is a world-leading independent research center in nanoelectronics and
nanotechnology. IMEC vzw is headquartered in Leuven, Belgium, has a sister company
in the Netherlands, IMEC-NL, offices in the US, China and Taiwan, and representatives
in Japan. Its staff of more than 1650 people includes about 550 industrial residents
and guest researchers. In 2008, its revenue (P&L) was estimated to EUR 270
IMEC's More Moore research aims at semiconductor scaling towards sub-32nm
nodes. With its More than Moore research, IMEC looks into technologies for nomadic
embedded systems, wireless autonomous transducer solutions, biomedical electronics,
photovoltaics, organic electronics and GaN power electronics.
IMEC's research bridges the gap between fundamental research at universities
and technology development in industry. Its unique balance of processing and
system know-how, intellectual property portfolio, state-of-the-art infrastructure
and its strong network worldwide position IMEC as a key partner for shaping
technologies for future systems.