Miniature Lighting Devices Developed Using Plasmons

quantum communications

Quantum communication systems of the future could utilize electromagnetic waves created on a layer of organic molecules and packaged as an on-chip light source.

A team of researchers, amongst them scientists from the Agency for Science, Technology and Research (A*STAR), Singapore, has captured minute flashes of light generated by an ultrathin layer of organic molecules inserted between two electrodes. They are hoping this technology could replace LEDs and lasers as signal sources for future ultrafast quantum computing and light-based communication systems that will be extremely small.

Plasmons are electromagnetic waves that skim along the interface between two materials. To investigate plasmons, a junction consisting of a layer of thiol molecules on a metal electrode with a top electrode made from liquid gallium-indium alloy was constructed by Christian A. Nijhuis from the National University of Singapore, in collaboration with Nikodem Tomczak from the A*STAR Institute of Materials Research and Engineering.

photonic device
Schematic of the ultracompact photonic sensor device. (Image credits: IEEE Photonics Technology Letters)

Plasmons were created by connecting a voltage across the thiol layer. Normally, thiol is an insulator but the layer was thin enough for electrons to move between the electrodes via quantum tunnels.  Plasmons on the thiol layer’s surface were exciting in the process. This resulted in them decaying into photons. Tomczak and his colleagues were able to observe these tiny pulses of light.

Tomczak was surprised by finding that the light came from very small spots that pulse at different frequencies, rather than from the whole junction. The light generated by the plasmons is polarized. The wavelength and polarization of the light can be controlled by using different molecules to form the organic layer, or by changing the voltage applied across the junction.

Tomczak notes that although more experimentation is required, the emission is similar to that from other single photon sources such as nanodiamonds or quantum dots. The pulsing also follows power-law statistics and is both polarized and diffraction limited.

Chu Hong Son and his team at the A*STAR Institute of High Performance Computing took the research a step further and modeled the spots as the product of a single dipole emitter which is the smallest possible source of light. The results confirmed the result achieved from the experiments and shows that the light is generated by plasmons decaying into a single photon.

Full research has been published in IEEE Photonics Technology Letters.