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Posted: September 1, 2010

Photonics: Silicon steps up

(Nanowerk News) Microelectronic devices such as computer processors and memory chips almost universally rely on silicon to control electrical currents. However, silicon's poor light-emitting properties have limited its use in photonics applications, and this has hampered progress in the integration of photonics devices with silicon electronics for optical communications on computer chips. Researchers from the A*STAR Institute of Microelectronics in Singapore have now demonstrated a light-detection system on a silicon chip that is capable of processing 320 gigabits per second (Gbps) — more than 600 times faster than USB 2.0 ports on present-day computers ("WDM multi-channel silicon photonic receiver with 320 Gbps data transmission capability").
Fabricating photonic devices with the sophisticated tools developed by the silicon electronics industry offers a number of benefits. "Using silicon for photonics devices offers good performances, ultra-compact size and very low cost," says Qing Fang from the research team.
The experimental set-up used to demonstrate multi-channel optical demultiplexing using germanium–silicon detectors integrated into a conventional silicon-based electronic circuit
Fig. 1: The experimental set-up used to demonstrate multi-channel optical demultiplexing using germanium–silicon detectors integrated into a conventional silicon-based electronic circuit.
Silicon-compatible detectors made from germanium have already been developed for optical signals. However, industry still awaits complete silicon-based photonic systems that can receive sufficient amounts of data for next-generation photonic systems.
In photonic devices, data transmission is significantly enhanced by the simultaneous use of multiple transmission channels: each channel uses a light beam with its own wavelength. To process that incoming mix of data, receivers need to separate the different wavelengths and guide each resultant beam into its own detector (Fig. 1).
The photonic receiver on a silicon chip developed by Fang and his co-workers can process light on 32 different wavelengths — comparable, for example, to the '32 bits' that can be processed simultaneously by modern microprocessors. The multi-channel receiver includes a 'demultiplexer' device that separates the 32 wavelengths and sends them to an array of germanium–silicon detectors, which capture the light for each channel. In the demultiplexer, light passes through an array of waveguides where interference effects focus light at each incoming wavelength to a different output channel connected to one of the germanium–silicon detectors (Fig. 1). As each detector can handle 10 Gbps, the researchers' device can achieve a transmission of data at 320 Gbps in total.
Before this technology can be used commercially, however, a number of technical problems must be resolved. For example, losses at the interface between the input waveguide and the optical fiber that transmits the light into the receiver are high because of their different sizes. Nevertheless, the successful proof-of-principle demonstration, says Fang, shows that "even based on the current technology, it is easy to realize high-speed data transmission up to terabit transmission rates on the silicon platform using this design."
Source: A*STAR
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