In a paper titled "Optical circulation in a multimode optomechanical resonator" published in Nature Communications, the researchers highlight that for the first time, an optical circulator was designed "magnet-free", relying on tiny mechanical vibrations imparted to a glass ring to directionally route light on an optical chip.
“Light propagation is symmetric in nature, which means if light can propagate from A to B, the reverse path is equally possible. We need a trick to break the symmetry”, explains AMOLF group leader Ewold Verhagen. “Usually this ‘trick’ is using centimetre-sized magnets to impart directionality and break the symmetric nature of light propagation. Such systems are difficult to miniaturize for use on photonic chips.”
Only a few micrometres across, the novel silica circulator allows light in the ring to interact with mechanical vibrations of the same structure, hence routing light uni-directionally between several ports.
“By shining light of a ‘control’ laser in the ring, light of a different color can excite vibrations through a force known as radiation pressure, but only if it propagates in the same direction as the control light wave”, Verhagen explains. “Since light propagates differently through a vibrating structure than through a structure that is standing still, the optical force breaks symmetry in the same way as a magnetic field would.”