LONDON Research institute IMEC (Leuven, Belgium) has reported a method to integrate high-speed CMOS electronics with nanophotonic circuitry based on plasmonic effects.
Metal-based nanophotonics can squeeze light into nanoscale structures that are much smaller than conventional optic components. This plasmonic technology, today still in an experimental stage, has the potential to be used in high-performance nanoscale optical interconnects for high performance computer chips, sensitive (bio)-molecular sensors, and efficient thin-film solar cells.
Plasmons are quasi-particles formed by oscillations in the free-electron gas within some materials. IMEC's results are published in the May issue of Nature Photonics.
The optical properties of nanostructured (noble) metals show great promise for use in nanophotonic applications, according to IMEC. When such nanostructures are illuminated with visible to near-infrared light, the excitation of collective oscillations of conduction electrons, so-called surface plasmons, generates optical resonances. These surface plasmons are capable of capturing, guiding, and focusing electromagnetic energy in deep-subwavelength distances. This is unlike conventional dielectric optical waveguides, which are limited by the wavelength of the light, and which therefore cannot be scaled down to tens of nanometers, IMEC added.
Nanoscale plasmonic circuits would allow massive parallel routing of optical information on ICs. But eventually that high-bandwidth optical information has to be converted to electrical signals. To make such ICs that combine high-speed CMOS electronics and plasmonic circuitry, efficient and fast interfacing components are needed that couple the signals from plasmon waveguides to electrical devices.
IMEC has demonstrated integrated electrical detection of highly confined short-wavelength surface plasmon polaritons in metal-dielectric-metal plasmon waveguides. The detection was done by embedding a photodetector in a metal plasmon waveguide. Because the waveguide and the photodetector have the same nanoscale dimensions, there is an efficient coupling of the surface plasmons into the photodetector and an ultrafast response. IMEC has set up a number of experiments that demonstrate this electrical detection. The measured polarization dependence, the experimentally obtained influence of the waveguide length and the measured spectral response are all in line with theoretical expectations, obtained from finite element and finite-difference-time-domain calculations.
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