Photonic chiral edge states are a unique class of electromagnetic modes that travel in only one direction and are immune to disorder-induced scattering.
The press release, issued by Franklin Hadley from Institute for Soldier Nanotechnology (MIT), explains in simple terms what we did.
Background
Chiral edge states were discovered around 30 years ago in quantum Hall effects in 2D electron gas. They are the underlying mechanism that supports dissipationless transport of electrons in quantum Hall systems and quantum spin Hall systems. Although they were only observed in fermionic systems, such as electrons in graphene, our work experimentally demonstrates, for the first time, that chiral edge states also exist for photonic systems.
A surprise in electromagnetics: achieving more by having less
Light can be confined and routed using structures known as waveguides. The slimmest waveguides, known as "single-mode waveguides", allow light to propagate only in one spatial configuration either in forward or backward direction. Using photonic chiral edge states, we can force light to propagate only in one spatial configuration and only in one direction, essentially creating "half-mode waveguides".
When the possibility of traveling backwards is eliminated, light exhibits fascinating and unparalleled properties. For instance, scattering can be completely suppressed, even in the presence of very large disorder:
Light field traveling in a chiral edge state from the left to the right. A metal obstacle is placed in the middle of the waveguide, but induces no reflection. |
As we increase the size of the obstacle, one can observe the electromagnetic energy route around the obstacle, along the edge of the topological photonic crystal (lower half of the array) that supports the chiral edge states. (Red denotes regions of high negative field amplitude, and blue denotes regions of high positive field amplitude) |
Additional movies contrasting the difference between conventional waveguides and the chiral edge states can be found here.
With a waveguide highly tolerant to large imperfection, a wide range of practical applications from electromagnetic isolation, to slow light and optical buffering may benefit.
How it works
Inspired by the earlier work of F. Duncan M. Haldane and S. Raghu, our first theory paper (Physical Review Letters) explained the general theory behind our photonic crystal structures.
An experimental demonstration
In our experimental paper (Nature), we adapted our structure to microwave frequencies and demonstrated complete suppression of disorder induced scattering of photonic chiral edge states.
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Additional high-res images download