Scientists control light flow with all-optical transistor
How light propagates is a question that weighs on the minds of many scientists. German and Swiss researchers have shed light on this problem by figuring out how to switch light all-optically on a chip. Presented online in the journal Science, they demonstrate a form of induced transparency enabled by radiation-pressure coupling of two modes: optical and mechanical. Their work, supported by a European Research Council (ERC) Starting Grant and a Marie Curie Excellence Grant, could result in a number of applications in telecommunications and quantum information technologies. The researchers from the Max Planck Institute of Quantum Optics (MPQ) in Germany and the Ecole Polytechnique Fédérale de Lausanne (EPFL) in Switzerland said an optomechanically induced transparency could be used for deceleration and on-chip storage of light pulses through microfabricated optomechanical arrays. Led by EPFL's Professor Tobias J. Kippenberg, the team found that the interaction of light (photons) and mechanical vibrations (phonons) helps control the transmission of a light beam past a chip-based optical micro-resonator directly by a second, more robust light beam. Past studies succeeded only in interacting laser light with atomic vapours through 'electromagnetically induced transparency' (EIT), which could control how light travels. Despite some interesting results, scientists found that EIT has a number of limitations including being restricted to light of wavelengths matching the natural resonances of atoms. For the purposes of their study, the German-Swiss team based their principle on optomechanical coupling of photons to mechanical oscillations inside an optical micro-resonator. They used basic nanofabrication methods to create optomechanical devices that have the capacity to simultaneously trap light in orbits and act as mechanical oscillators. Radiation pressure, which occurs when phonons exert force, results when light is coupled with the resonator. Despite having used this force for years to trap and cool atoms, scientists started recognising its potential to control mechanical vibrations at the micro- and nanoscale only within the last five years. This gave way to the birth of cavity optomechanics, a research field that focuses on unifying photonics and micro- and nanomechanics. The team found that the radiation pressure force is bolstered within an optical micro-resonator and can deform the cavity, effectively coupling the light to the mechanical vibrations. Another 'control' laser can also be coupled to the resonator. The researchers discovered that the beating of two lasers triggers vibration of the mechanical oscillator, and in turn stops the signal light from entering the resonator by an optomechanical interference effect. This results in a transparency window for the signal beam. Dr Schliesser from both the EPFL and MPQ says, 'We have known for more than two years that the effect existed.' Adds Stefan Weis, who is also from both institutions and one of the lead authors of the paper: 'Once we knew where to look it was right there.' The effect, dubbed 'OMIT' (optomechanically induced transparency) by the scientists, could offer the research world new and improved functionality of photonics. According to the team, future developments based on OMIT could help convert a stream of photons into mechanical excitations (phonons); realise optical buffers that enable extended optical information storage; and benefit hybrid quantum systems.
Countries
Switzerland, Germany