An international research consortium has demonstrated
all-optical signal processing on silicon above 100Gbit/s.
"This is the fastest silicon photonic optical signal processing
demonstrated to date," claimed Belgian research lab IMEC. "This
experiment proved the viability of silicon-organic hybrid [SOH]
waveguides for all-optical processing of broadband
telecommunication signals."
The key element is a waveguide with fast highly non-linear
performance.
In this case it was fabricated by combining deep-ultraviolet
lithography, standard CMOS processing and organic molecular beam
deposition.
In this case the 4mm long waveguide has a non-linearity
coefficient of 105/(W.km) in the 1.55um
telecommunication window
"Based on these waveguides, all-optical demultiplexing of a
170.8Gbit/s telecommunication signal to 42.7Gbit/s was performed
using four-wave mixing," said IMEC.
The team included collaborators from the
University of
Karlsruhe, Germany; IMEC, Belgium;
Lehigh University,
USA and ETH Zurich,
Switzerland.
All-optical processing removes the need for optical to
electronic, and electronic to optical, conversions - potentially
cutting cost if it can be done without exotic materials.
Silicon-based technology, in particular silicon-on-insulator,
can be used for the fabrication of passive linear optical devices
such as filters, however slow dynamics caused by unwanted
non-linear effects hamper all-optical switching in silicon.
"So far, the data rate achieved by using bare silicon waveguides
was limited to only 40Gbit/s," said IMEC. "The SOH approach
overcomes this intrinsic limitation 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 exhibit optical interaction without introducing
significant absorption and a key feature of this organic material
and the deposition process is its ability to homogeneously fill the
slot between the waveguides.
The silicon circuits were designed by the University of
Karlsruhe and were fabricated on IMEC's European funded
multi-project
200mm silicon photonics
platform.
A vapour-deposited organic film covering a silicon
waveguide patterned on a silicon-on-insulator
substrate.