Plasmonic Modulators Could Work as Submicron Switches

Nanomechanical plasmonic phase modulators could be used as optical switches with footprints smaller than one square micron, potentially allowing densely packed photonic chips.

Researchers at Rutgers University and the National Institute of Standards and Technology (NIST) demonstrated that an optical signal can be modulated in a 200-nm-high waveguide. The signal’s phase is modulated as it passes through an air gap between two gold layers, when a force generated by the device slightly deforms the top gold layer.

A free-space excitation laser (vertical light on the right) couples to gap plasmons (alternating red and blue light) in a gold-air-gold nanofabricated waveguide. The plasmons propagate through the waveguide under free-floating micro-beams in the top gold layer (color coded to show depth). When the beams are electrically actuated towards the bottom gold layer, effective refractive index of the waveguide increases, phase-retarding the plasmons. Courtesy of Dr. Brian Dennis, Rutgers University.

When one of these modulators is placed next to a similar static device, it could act as a 2 × 2 switch, based on evidence reported elsewhere of coupling between adjacent waveguides. The technology could also be useful for electrically tunable plasmonic devices.

The scientists experimentally verified such devices in a 23-μm-long waveguide with a gap in the range of 200 nm; they cite computer modeling to make a case that the waveguides can be scaled down to as little as 1 μm long with a 20-nm gap without significant loss, meaning optical switches could be scaled down to the dimensions of electronic devices.

In contrast, established optical switching technologies based on microelectromechanical systems (MEMS), lithium niobate and silicon and electro-optic polymer plasmonic technologies have active elements in scales up to hundreds of microns.

The research was published in Nature Photonics (doi: 10.1038/nphoton.2015.40).

For more information, visit www.rutgers.edu.