A photonic device that emits light only in one direction has been created by researchers. They created their device by carefully tailoring the shape of a set of etched silica bars – thereby using topology to modify a curious effect that was predicted 90 years ago. The light source could have multiple applications in optoelectronics.
A key challenge in creating photonic device circuits is that light will happily travel in both directions through optical devices – which causes unwanted effects. Current solutions such integrating a mirror to reflect light travelling in the wrong direction tend to be bulky, inefficient or difficult to fabricate. Now, researchers in China and the US have put a topological twist on an effect first proposed in 1929 and created a photonic crystal that emits light in only one direction.
Creating experimental systems that exhibit “bound states in the continuum” (BICs) remained a mathematical curiosity for several decades. Beginning in the 1970s, researchers realized that the same physics applied beyond quantum mechanics and more broadly to systems of waves. Since then, BICs have been observed in light, sound and water waves as well as surface waves in graphene.