Chiral Metasurfaces and Optical Chirality

Chiral metasurfaces are ultrathin, two-dimensional assemblies of subwavelength resonators whose lack of mirror symmetry gives rise to strong differential responses to left- and right-handed circularly polarised light. By engineering the geometry and arrangement of dielectric or plasmonic meta-atoms, it is possible to tailor optical chirality—namely, the capacity of a structure to distinguish and interact selectively with the helicity of electromagnetic waves. Modern approaches exploit geometric-phase engineering, bound states in the continuum (BIC) and symmetry breaking in three dimensions to enhance circular dichroism, rotate the plane of polarisation (optical activity) and achieve high quality-factor resonances. Such capabilities underpin a growing array of applications, from enantiomeric sensing and chiral lasers to spin-controlled holography, nonlinear frequency conversion and optical communications. Advances in loss-minimised dielectric platforms and novel fabrication strategies have shifted the field towards robust, tunable and CMOS-compatible devices that promise transformative impact in photonics, chemistry and quantum information.

Research from Nature Portfolio

Researchers have demonstrated planar chiral metasurfaces that support electromagnetic bound states in the continuum, achieving ultra-high resonance quality factors and near-unity circular dichroism at optical frequencies. By employing symmetry-reduced meta-atoms with high birefringence and winding elliptical eigenstate polarisations of opposite helicity, both linear and near-field nonlinear chiroptical responses can be tuned via in-plane symmetry breaking or variation of illumination angle. These metasurfaces pave the way for compact chiral lasers, ultrasensitive filters and active metadevices with sharply resonant circular polarisation control. In a complementary approach, the concept of chirality-assisted geometric phase has been introduced to decouple and independently address all four circular-polarisation output channels. This allows arbitrary wavefront shaping for each co-polarised channel, as exemplified by multi-beam refraction and the generation of orbital angular momentum modes with distinct topological charges, thereby opening new opportunities for reconfigurable beam steering and multiplexed wireless links. Earlier work has also shown that three-dimensional chiral relief patterned in monocrystalline silicon by focused-ion-beam lithography can yield durable visible-light metasurfaces combining high transmittance (50–80 %), moderate circular dichroism and tens of degrees of optical rotation, confirming the viability of silicon-based chiral platforms.

Chiral Metasurfaces and Optical Chirality publication trend

The graph below shows the total number of articles in chiral metasurfaces and optical chirality across all publications each year (not limited to Nature Index journals).

Technical terms

Chiral metasurface: A planar array of mirror-asymmetric meta-atoms that interacts differently with left- and right-handed circularly polarised light.

Optical chirality: A property of electromagnetic fields or materials that quantifies differential interaction with opposite helicities of circularly polarised light.

Circular dichroism: The difference in absorption or transmission between left- and right-handed circularly polarised light by a chiral medium.

Bound state in the continuum (BIC): A localized resonant mode embedded within the continuum of radiating states, exhibiting a theoretically infinite quality-factor in the absence of perturbations.

Geometric phase: A polarisation-dependent phase shift imparted by spatially varying anisotropic structures, independent of optical path length.

Quality factor (Q-factor): A dimensionless measure of resonance sharpness defined as the ratio of stored to dissipated energy per oscillation cycle.

References

1. Planar chiral metasurfaces with maximal and tunable chiroptical response driven by bound states in the continuum. Nature Communications (2022).
2. Independent phase modulation for quadruplex polarization channels enabled by chirality-assisted geometric-phase metasurfaces. Nature Communications (2020).
3. Chiral visible light metasurface patterned in monocrystalline silicon by focused ion beam. Scientific Reports (2018).
4. Unlocking the out-of-plane dimension for photonic bound states in the continuum to achieve maximum optical chirality. Light: Science & Applications (2023).
5. Dual-band polarized upconversion photoluminescence enhanced by resonant dielectric metasurfaces. eLight (2023).
6. Chiral Bound States in the Continuum in Plasmonic Metasurfaces. Laser & Photonics Review (2023).