- Demonstrates high-speed operation by integrating light source and
optical modulator on the same silicon chip using structure that
obviates need for thermal control mechanism -
Kawasaki, Japan, August 31, 2012 - Fujitsu Laboratories Limited
today announced the development of an integrated silicon optical
transmitter for use in an optical transceiver(1), which is essential
for enabling large volumes of data to be transmitted between CPUs.
Thermal fluctuations from the heat emitted by CPUs have a large
impact on both the light source built into optical transmitters
located near CPUs and the optical modulators(2) that encode data
into the light emitted from the light source. This means a thermal
control mechanism has been required to ensure that the operating
wavelengths of both the light source and optical modulator
consistently match. Fujitsu Laboratories previously devised a
structure incorporating both the light source and optical modulator
that did not require thermal control and demonstrated identical
thermal properties by using separate prototypes of the light source
and the optical modulator. This time, using the same structure to
make a prototype optical transmitter that integrates the light source
and optical modulator on the same silicon chip, Fujitsu Laboratories
demonstrated that it could achieve optical modulation signals at
speeds of 10 Gbps at temperatures ranging from 25 degrees celsius to
60 degrees celsius without a thermal control mechanism. Moreover,
the overall electricity consumed by the optical transmitter was
reduced by roughly half compared to previous methods.
This technology enables compact, low-power optical transceivers
to be mounted directly in CPU packaging. Through its application
exaflops-class supercomputers(3) and high-end servers requiring
high-speed transmission of large volumes of data, the technology
paves the way for super-high-speed computers.
<Background>
In recent years, supercomputer performance has been roughly
doubling every 18 months. Right now, work is underway to produce
exaflops-class supercomputers with a target date around 2020. The
creation of these ultrafast computers will require high-volume data
transmission technology that allows individual CPUs to transfer data
to each other at tens of terabits per second. With existing
electrical interconnects based on copper wire, however, the dramatic
increases required in circuit space, number of transmission lines,
and electricity consumption in accordance with the higher data volumes
are thought to make it difficult to achieve the data transmission
speeds needed for exaflops-class supercomputers. As a result,
consideration is being given to the use of optical interconnect
technology in which, as shown in figure 1, CPUs are connected using
light. Recently, in particular, attention is being focused on the
development of silicon photonics(4) technology enabling optical
transceivers to be compact and densely integrated, and that enables
integration of electrical and optical components.
<Technological Issues>
The transmitter component of an optical transceiver comprises a
light source and an optical modulator that encodes data into the light
emitted by the light source. A good candidate for the optical modulator
is a ring resonator(5), as it is compact and energy efficient. But
because the optical transceiver is located near the CPU, the lasing
wavelength and the operating wavelength of the ring-resonator-based
optical modulator do not coincide with each other due to heat from the
CPU, resulting in information not being encoded in the light. A
thermal control mechanism is needed to ensure that they match exactly,
which, however, is an obstacle to making the transceiver compact and
energy efficient.
<Resolution Approach>
By using the same ring resonator for both the wavelength control unit
of the light source and the optical modulator, Fujitsu Laboratories
previously devised a structure that made the wavelengths of the light
source and optical modulator identical without the need for a thermal
control mechanism. It used this structure to build separate prototypes
of the light source and optical modulator, and it previously
demonstrated that their thermal properties were identical.
<Newly Developed Technology>
This time Fujitsu Laboratories made a prototype optical transmitter
that integrates on the same silicon chip a light source and optical
modulator employing the previously devised structure. Using this
transmitter, it demonstrated that it could make the wavelengths of
the light source and optical modulator identical without the need
for a thermal control mechanism and could achieve optical modulation
signals at speeds of 10 Gbps at temperatures ranging from 25 degrees
celsius to 60 degrees celsius.
Figure 2 depicts the prototype silicon optical transmitter that
integrates the light source and optical modulator. To enable shifts
in the wavelengths caused by temperature changes to match, the same
ring resonator is used for both the wavelength control unit of the
light source and the optical modulator. Moreover, to safeguard
operation even if there are slight differences in the wavelengths of
the light source and optical modulator, the optical modulator is
structured with an alignment of multiple ring resonators, increasing
the operating wavelength range. Using this structure, there is no
need for a thermal control mechanism, and the overall electricity
consumed by the optical transmitter was reduced by roughly half
compared to previous methods. It is compact, measuring roughly only
2 mm long without the semiconductor optical amplifier. Through
optimization using the silicon wire optical waveguide structure(6),
it is expected that in the future the size can be reduced to under
1 mm.
Figure 3 depicts the optical modulation signals measured at speeds
of 10 Gbps at varying temperatures. When varying the temperature from
25 degrees celsius to 60 degrees celsius, the spectrum's peak wavelength
moves to the long-wavelength side, but a stable modulation signal is
derived without controlling the wavelengths.
By further increasing the speed of this optical transmitter and
integrating multiple transmitters on one chip using wavelength
multiplexing technology, it will be possible to create optical transmitters
small enough to be embedded into CPU modules capable of transmitting
large volumes of data at rates of several terabits per second.
<Results>
The use of this technology enables the development of exaflops-class
supercomputers and high-end servers requiring energy efficient
transmission of large volumes of data between CPUs, thereby paving the
way for super-high-speed computers.
<Future Plans>
Fujitsu Laboratories plans to continue development of the optical
receiver using the same silicon photonics technology, and will integrate
it and this new transmitter to create a compact optical transceiver.
Moreover, by applying wavelength multiplexing technology and pursuing
dense integration, it will work on developing large-capacity integrated
optical interconnects capable of enabling data transmission speeds of
tens of terabits per second.
<Glossary and Notes>
1 Optical transceiver:
A module that converts an electrical signal to an optical signal, which
it then transmits, and that also receives an optical signal and converts
to an electrical signal.
2 Optical modulator:
An optical component that converts electrical signals to optical
signals. These include intensity modulators that convert to an
optical-intensity signal and phase modulators that convert to light-phase
signals.
3 Exaflops-class supercomputer:
A supercomputer that can process 10 to the18th "FLoating-point number
Operations Per Second."
4 Silicon photonics:
Technology in which a photonic device is configured on a silicon
substrate. By using silicon, the optical circuits can be made smaller,
enabling dense integration. It also has other merits, such as the
ability to configure optical circuits and electrical circuits in one
unit, and lower manufacturing costs.
5 Ring resonator:
A resonator made of a ring-type optical waveguide. When used in
silicon photonics, this can be made extremely small, with a radius on
the order of microns. The ring's resonance effect makes it possible to
create a highly efficient optical modulator.
6 Silicon wire optical waveguide structure:
An extremely small silicon optical waveguide, in which the height and
width of the cross-sectional surface is less than 1 micrometer.
<About Fujitsu>
Fujitsu is the leading Japanese information and communication technology (ICT)
company offering a full range of technology products, solutions and services.
Over 170,000 Fujitsu people support customers in more than 100 countries. We
use our experience and the power of ICT to shape the future of society with
our customers. Fujitsu Limited (TSE:6702) reported consolidated revenues of
4.5 trillion yen (US$55 billion) for the fiscal year ended March 31, 2011.
For more information, please see http://www.fujitsu.com.
<About Fujitsu Laboratories>
Founded in 1968 as a wholly owned subsidiary of Fujitsu Limited,
Fujitsu Laboratories Limited is one of the premier research centers in the
world. With a global network of laboratories in Japan, China, the United States
and Europe, the organization conducts a wide range of basic and applied
research in the areas of Next-generation Services, Computer Servers, Networks,
Electronic Devices and Advanced Materials. For more information,
please see: http://jp.fujitsu.com/labs/en.
<Press Contacts>
Fujitsu Limited
Public and Investor Relations Division
Inquiries: https://www-s.fujitsu.com/global/news/contacts/inquiries/index.html
<Technical Contacts>
Fujitsu Laboratories Ltd.
Next-Generation Manufacturing Technologies Research Center
E-mail: si-photonics-2@ml.labs.fujitsu.com
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