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Predicting noise in photonic circuits

Researchers at the Moscow Institute of Physics and Technology believe it will be possible to predict accurately the level of noise caused by the amplification of photonic and plasmonic signals in nanoscale optoelectronic circuits. The scientists say their approach could be used not only to evaluate the ultimate data transfer rates in emerging optoelectronic devices, but also to discover the fundamental bandwidth limitations of nanophotonic interfaces.

The main obstacle faced by plasmonics is said to be signal attenuation. Due to high losses, surface plasmons can only propagate over long distances in active plasmonic waveguides. While these guide the plasmonic signal from the transmitter to the receiver, they also amplify it using the electrical energy flowing through the device. However, amplification also adds unwanted random signals – or noise.

Researcher Dmitry Fedyanin said: “Signal amplification inevitably decreases the signal-to-noise ratio and the more gain an amplifier provides – or, in our case, the greater the signal loss it needs to compensate for – the more noise it produces. This problem is especially pronounced in plasmonic waveguides with gain.”

Because noise causes errors during transmission, it reduces the effective data transfer rate due to the need for error correction. Error control also requires additional on-chip components, making new devices more difficult to design and manufacture.

"If we know the noise power in a nanophotonic communication channel, as well as its spectral characteristics, it is possible to evaluate the maximum data transfer rate along that channel,” researcher Andrey Vyshnevyy pointed out. “Furthermore, we can identify ways to reduce noise by choosing certain regimes of device operation and by using optical and electrical filtering techniques."

The theory targets a new class of device, which combines the advantages of electronics and photonics. In such a chip, plasmonic components would be used for ultrafast communication between processor cores and registers. Although signal attenuation was previously regarded as the proposed chip's main drawback, the Russian study shows that, as soon as the loss of signal has been compensated, a way must be found to deal with noise. If not, the signal might get drowned by spontaneous emissions, making the chip virtually useless.

The researchers’ calculations are said to show that an active plasmonic waveguide with a cross section of 200 × 200nm could be used to transmit signals over a distance of 5mm at more than 10Gbit/s per spectral channel.

Concluding, they believe it will be possible to create a device which combines miniature size and low error count with high data transfer rates and relatively high energy efficiency. And this ‘plasmonic breakthrough’ could come in the next 10 years.

Peggy Lee

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