Due to the voltage applied, a beam of light (top left) is modulated by the digital bits (bottom right) of the converter (yellow). An electrical signal is converted into an optical signal.
Credit: A. Melikyan/KIT
Thanks to optical signals, mails and data can be transmitted
rapidly around the globe. But also exchange of digital information between
electronic chips may be accelerated and energy efficiency might be increased by
using optical signals. However, this would require simple methods to switch
from electrical to optical signals. In the journal Nature Photonics,
researchers now present a device of 29 µm in length, which converts signals at
a rate of about 40 gigabits per second. It is the most compact high-speed phase
modulator in the world
"Conversion of electrical into optical signals happens
closer to the processor," Juerg Leuthold says. He coordinated the research
project at the Karlsruhe Institute of Technology and has meanwhile moved to the
ETH Zurich .
"As a result, speed gains are achieved and conduction losses can be
prevented. This might reduce energy consumption of the growing information
technology."
The electro-optical converter consists of two parallel gold
electrodes of about 29 µm in length, which is one third of the diameter of a
human hair. The electrodes are separated by a gap of about one tenth of a
micrometer in width. The voltage applied to the electrodes is synchronized with
the digital data. The gap is filled with an electro-optical polymer, whose
refraction index changes as a function of the applied voltage. "A
continuous beam of light from the silicon waveguide excites electromagnetic
surface waves, so-called surface plasmons (SP), in the gap," Argishti
Melikyan, KIT, first author of the publication, explains. "As a result of
the voltage applied to the polymer, the phase of the SP is modulated. At the
end of the device, the modulated SP enter the exit silicon waveguide in the
form of a modulated beam of light. In this way, the data bits are encoded in
the phase of the light."
Their recent results revealed that the electro-optic
modulator reliably converts data flows of about 40 gigabits per second. It uses
the infrared light of 1480 -- 1600 nanometers in wavelength usually encountered
in the broadband glass fiber network. Even temperatures of up to 85°C do not
cause any operation failures. The presented device is the most compact
high-speed phase modulator in the world. It can be produced by well-established
CMOS fabrication processes. Integration into current chip architectures is
hence possible. "The device combines many advantages of other systems,
such as a high modulation speed, compact design, and energy efficiency. In the
future, plasmonic devices might be used for signal processing in the terahertz
range," says Christian Koos, spokesperson of KIT's Helmholtz International
Research School of Teratronics (HIRST), which focuses on merging photonic and
electronic techniques for high-speed signal processing. "Hundreds of
plasmonic modulators might fit on a chip and data rates in the range of
terabits per second might be reached."
Presently, information and communication systems consume
about 10 percent of the electricity in Germany . This includes computers
and smartphones of individual users as well as servers at large computing
centers. As data traffic grows exponentially, new approaches are required to
increasing the capacity of such systems and reducing their energy consumption
at the same time. Plasmonic components might be of decisive importance in this
respect.
The present paper is part of the EU project NAVOLCHI, Nano
Scale Disruptive Silicon-Plasmonic Platform for Chip-to-Chip Interconnection.
This project is aimed at using the interaction of light and electrons in metal
surfaces for the development of novel components for data transmission between
chips. "Conventional electric chip-to-chip data transmission reaches its
limits," says the present project coordinator Manfred Kohl, KIT.
"NAVOLCHI is about to overcome those limits using optical technology."
It is funded under the 7th Research Framework Programme of the EU and has a
budget of EUR 3.4 million.
Story Source:
The above story is based on materials provided
by Karlsruhe Institute of Technology. Note:
Materials may be edited for content and length.
Journal Reference:
A. Melikyan, L. Alloatti, A. Muslija, D. Hillerkuss, P. C.
Schindler, J. Li, R. Palmer, D. Korn, S. Muehlbrandt, D. Van Thourhout, B.
Chen, R. Dinu, M. Sommer, C. Koos, M. Kohl, W. Freude, J. Leuthold. High-speed
plasmonic phase modulators. Nature Photonics, 2014; DOI: 10.1038/NPHOTON.2014.9
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