An electronic diode is a nonlinear semiconductor circuit component that allows conduction of electrical current in one direction only. A component with similar functionality for electromagnetic waves, an electromagnetic isolator, is based on the Faraday effect of the polarization state rotation and is also a key component of optical and microwave systems. Here we demonstrate a chiral electromagnetic diode, which is a direct analogue of an electronic diode: its functionality is underpinned by an extraordinary strong nonlinear wave propagation effect in the same way as electronic diode function is provided by a nonlinear current characteristic of a semiconductor junction. The effect exploited in this new electromagnetic diode is an intensity-dependent polarization change in an artificial chiral metamolecule. This microwave effect exceeds a similar optical effect previously observed in natural crystals by more than 12 orders of magnitude and a direction-dependent transmission that differing by a factor of 65
Shadrivov and co at the Australian National University in Canberra say it is possible to create diode-like behaviour using metamolecule made of two wires separated by a dielectric sheet and rotated relative to each other.
A microwave passing through wires generates currents in each that tend to interact. At certain frequencies these currents re-reinforce or cancel out. Adding a nonlinear diode to one of the wires makes the effect of the metamolecule nonlinear too.
The result is a device that acts as a diode for right-handed polarized light of a specific frequency, but is entirely transparent to left-handed polarized light. The direction of permissible transmission depends on the frequency of the microwaves. And the chirality of the device can be reversed by changing the relative angle of the wires.
The transmission curve shows a hysteresis effect. That means the actual intensity of the transmitted light takes different values for the same input, depending on the history of the device. If that sounds familiar it’s because a very similar type of behaviour occurs in memristors.
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