Abstract
AbstractOne of the most fascinating properties of chiral molecules is their ability to rotate the polarization of light. Since Faraday's experiments in 1845, it has been known that nonreciprocal polarization rotatory power can be induced by a magnetic field. But can reciprocal polarization rotation in chiral molecules be influenced by an electric field? In the 1960s, Aizu and Zheludev introduced the phenomenon of electrogyration. While the linear (Pockels) and quadratic (Kerr) electro‐optical effects describe how an external electric field changes linear birefringence and dichroism, electrogyration describes how a field changes the circular birefringence and dichroism of a medium. Electrogyration is observed in dielectrics, semiconductors, and ferroelectrics, but the effect is small. This work demonstrates a nanostructured photonic metamaterial that exhibits quadratic electrogyration—proportional to the square of the applied electric field—six orders of magnitude stronger than in any natural medium. Giant quadratic electrogyration emerges as electrostatic forces acting against forces of elasticity change the chiral configuration of the metamaterial's nanoscale building blocks and consequently its polarization rotatory power. This observation of giant electrogyration alters the perception of the effect from that of an esoteric phenomenon into a functional part of the electro‐optic toolkit with application potential.
Highlights
Optical activity manifests itself as circular birefringence - rotation of the polarization state of light, and circular dichroism - differential transmission of circularly polarized waves
Faraday discovered that optical activity can be changed by an external magnetic field, but it took another 117 years until the electrical counterpart of the Faraday effect was found in ferroelectric crystals, where optical activity was changed by an external electric field.[1]
Local and non-local electro-optic effects In linear optics the constitutive equation for the electric field displacement D ω induced in a medium by a light wave E ω with frequency ω and wave vector k is given by DωεωEω ikΓ ω E ω
Summary
Optical activity manifests itself as circular birefringence - rotation of the polarization state of light, and circular dichroism - differential transmission of circularly polarized waves. Faraday discovered that optical activity can be changed by an external magnetic field, but it took another 117 years until the electrical counterpart of the Faraday effect was found in ferroelectric crystals, where optical activity was changed by an external electric field.[1] At around the same time, K. Zheludev independently described this phenomenon, naming it gyroelectric effect or electrogyration.[2,3] The Faraday effect is non-reciprocal, i.e. the optical rotation continues to grow when the wave’s propagation direction is reversed. Optical activity and electrogyration are reciprocal, i.e. optical rotation is compensated upon reversal of the propagation direction. Many chiral metamaterials have been shown to exhibit optical activity exceeding that of natural materials by several orders of magnitude, but the complex geometry of these typically three-dimensional (3D)
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