Practical Y-splitter channels plasmons

03 Oct 2008

Miniaturized photonic circuits could benefit from a cleverly designed Y-splitter that steers surface plasmon polaritons.

Y-splitter design

A European project developing micro- and nano-scale photonic components based on metal/polymer structures has built the first practical Y-splitter for surface plasmon polaritons (SPPs). The project is looking at the commercial viability of such devices with French component maker Silios Technologies (Optics Express 16 14369, Optics Express 16 13585).

"We show that basic passive components such as Y-splitters can be fabricated reliably using mass-production compatible technology," Anatoly Zayats, PLASMOCOM project coordinator, told optics.org. "Our aim is to develop miniaturized photonic circuits based on SPPs. Such circuits offer lower fabrication cost, enhanced dynamic and active functionality with lower electric consumption power than conventional nanophotonic circuits."

Plasmonic waveguides are considered a promising alternative to optical waveguides in future highly integrated photonic devices, since the close confinement property of SPPs can improve efficiency.

Although a Y-splitter for SPPs has already been suggested, the device suffered from excess losses at the point at which it splits into two branches. "Current fabrication techniques are limited and introduce a defect in the branching region," explained Zayats. "The defect causes some of the light to scatter and has so far prevented such Y-splitters from finding practical applications."

Now, the European group proposes a modified Y-splitter design that introduces a 520 nm gap in the left arm of the Y-splitter at the branching point. The branches measure 7 µm in length, with a separation of 3 µm between the output arms. "By changing the shape of the region where the two output waveguides emerge from the splitting region, we reduce the scattering losses that are caused by the defect," explained Zayat.

In the device, a plasmon wave propagates along the straight part of the Y splitter. When it encounters the splitting region it is scattered, but due to the guiding conditions it cannot escape from the waveguide and travels along the branches. Although scattering results in some losses via plasmon radiation, these losses are relatively small.

"While the design is not ideal and still suffers from some loss, it is a design that can actually be manufactured," commented Zayats. "The ideal design may involve very tiny elements that cannot be made with current technologies."

The next step for the PLASMOCOM project is to combine passive and active plasmonic components to control signals propagating through the elements. The ultimate goal for the group is to build integrated plasmonic circuits, analogous to today's electronic chips.