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Fujitsu Cuts Optical Switch Power Consumption in Half

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KAWASAKI, Japan, Nov. 10, 2010 — Fujitsu Laboratories Ltd. announced its new optical waveguide switch consumes only half the power of a traditional switch through the use of fine-patterned silicon germanium instead of traditional silicon in the refractive-index modulator.

Just as data volume being transmitted over networks is increasing constantly, so too is the power consumption of networking equipment, leading to concerns for a potentially serious energy problem in the future. The amount of energy consumed by networking equipment in 2025 is predicted to be 13 times that of 2006 levels if nothing changes, according to a December 2007 report by the Japan Ministry of Economy, Trade and Industry. Fujitsu said its new technology will allow for high-speed optical switches capable of operating across a wide range of wavelengths to support demanding services such as ultrahigh-definition videoconferencing, while also requiring very little power.

Figure 1: Next-generation network using optical switches. (Images: Fujitsu)

Conventionally, switching between optical network paths requires that signals be converted from light to electricity and back again to light in order to be processed - conversions that consume considerable amounts of power. An optical switch that processes optical signals as they are - without the need for conversion - would greatly reduce its power requirements. This issue has spurred ongoing research and development efforts for next-generation networks (Figure 1).

A waveguide optical switch is a design that arrays multiple optical switching elements in series, between an optical-signal input point and output point. By combining the operations of each optical switching element, a desired optical signal path can be created (Figure 2).

Figure 2: Optical waveguide switch employing silicon photonics technology.

An optical waveguide switch based on silicon (Si) photonics can be inexpensively mass produced through well-established silicon fab techniques. Optical switches based on nanometer-scale waveguides and control electronic circuits can be lined up in large numbers on the same substrate, and large-scale optical switches can be fabricated compactly, measuring a mere few centimeters squared.

Large-scale optical-waveguide switches operate multiple optical switching elements simultaneously. The heat that this generates can degrade device performance, which necessitates the lowest possible power consumption for each optical switching element.

Figure 3: Top-view of optical switching element

With optical switching elements, the application of an electrical current to the refractive-index modulator causes electrons to accumulate in fine waveguides, which modulates the refractive index and switches the output port (Figure 3). With conventional optical switching elements made using fine-patterned Si, the electron-accumulation efficiency in fine Si waveguides is low, necessitating more current to achieve sufficient electron-accumulation and increasing power consumption.

Fujitsu said it has developed the first optical switching element that uses fine-patterned silicon germanium (SiGe) in the refractive-index modulator (Figure 4). Forming fine-patterned SiGe, which has a narrower bandgap than Si, on top of Si allows for more efficient electron accumulation with less power required for switching.

Figure 4: Cross-sectional view of Fujitsu's new refractive-index modulator that uses fine-patterned silicon germanium (SiGe).

Fujitsu said its prototype optical switch devices operate on 1.5 mW of power, approximately half the power required for conventional fine-patterned Si optical switching elements. This represents the lowest power requirement to date for an optical switching element capable of high-speed operation across a wide range of wavelengths, the company said.

Details of Fujitsu's technology were presented this week at the 23rd Annual Meeting of the IEEE Photonics Society (PHO 2010) in Denver.

The company said it will now work to develop integration technologies to create large-scale optical switches to enable next-generation networks.

Parts of the research were undertaken as part of the work of the Vertically Integrated Center for Technologies of Optical Routing Toward Ideal Energy Savings (VICTORIES) project, under The Formation of Innovation Center for Fusion of Advanced Technologies, sponsored by the Special Coordination Funds for Promoting Science and Technology of Japan's Ministry of Education, Culture, Sports, Science and Technology (MEXT).

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Nov 2010
In a semiconductor material, the minimum energy necessary for an electron to transfer from the valence band into the conduction band, where it moves more freely.
A charged elementary particle of an atom; the term is most commonly used in reference to the negatively charged particle called a negatron. Its mass at rest is me = 9.109558 x 10-31 kg, its charge is 1.6021917 x 10-19 C, and its spin quantum number is 1/2. Its positive counterpart is called a positron, and possesses the same characteristics, except for the reversal of the charge.
Electromagnetic radiation detectable by the eye, ranging in wavelength from about 400 to 750 nm. In photonic applications light can be considered to cover the nonvisible portion of the spectrum which includes the ultraviolet and the infrared.
See acousto-optic modulator; electro-optic modulator.
Systeme Internationale d'Unites, the international metric system of units.
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