Nanophotonic chips come a step closer

Photonic integrated devices can vastly increase the speed of computing, revolutionise consumer electronics and provide new minimally invasive diagnostics for early disease detection. Within RE-ACT (Novel active nanophotonic devices in rare-earth doped double tungstates), researchers set the stage for fabricating highly integrated photonic circuits. A major focus was on inexpensive fabrication techniques compatible with complementary metal-oxide semiconductor technology.

To realise nano-scale photonic devices that match the size of electronic components, researchers considered the use of plasmonics. This is a nanophotonic approach that allows the control of light on the nanometre scale. The team combined plasmonic waveguides with crystalline potassium double tungstate (KREW) doped with rare-earth ions.

KREW is a crystalline material that can provide stable gain at different wavelengths. Researchers used heterogeneous techniques to integrate KREW into different substrates such as silicon dioxide and silicon. They focused on studying bends in KREW waveguides and how plasmonic effects can reduce propagation losses in sharp bends.

Researchers experimentally demonstrated that the introduction of a thin metal layer underneath the core of the waveguide reduces overall bend losses. The study can be applied to any waveguide with low refractive index contrast.

Another project activity was the development of surface-enhanced Raman spectroscopy (SERS) sensors integrated on top of optical waveguides. Such sensors can serve to monitor wastewater toxicity. Future initiatives may use plasmonic nanoparticles and passive waveguides to realise SERS sensors for detecting contaminants in drinking water.

The possibility to integrate on the chip nano-scale photonic devices with increased functionality, almost unlimited bandwidth and very low power consumption opens the door to new and exciting applications.