A single theoretical and simulation study explores how metal–insulator–metal cavities can confine optical vortices far below the illuminating wavelength. Reflected surface waves build resonances that strengthen the field. Some calculated ring radii fall below one sixtieth of the wavelength, while losses and quantum effects set limits as the gaps approach atomic scales. No working device was demonstrated.
A peer-reviewed Nature Communications study uses theory and full-wave electromagnetic simulations to investigate tightly confined optical vortices. These light fields have a phase that winds around their centre. The proposed geometry places an insulating gap between metal surfaces. Surface plasmons, coupled oscillations of light and electrons at the interface, have a shorter wavelength there than the incoming illumination, allowing a smaller spatial pattern.[1]
Waves reflected at the cavity boundary form standing-wave resonances and enhance the local field. The calculations produce vortex footprints below one tenth of the illumination wavelength, with inner-ring radii below one sixtieth in some configurations. The spiral geometry and incident light together control the phase winding. These sizes describe calculated structures under the model’s chosen material and geometric assumptions, rather than measurements from a fabricated device.[1]
Metal losses, the precision needed to fabricate the gap and quantum effects constrain the design. At atomic-scale separations, electron tunnelling and nonlocal response become significant; making the gap ever narrower does not guarantee a stronger standing wave. Molecular sensing and interactions between light and handed molecular structures are possible directions discussed by the authors. Their performance remains to be tested experimentally, beyond the present theoretical and simulation results.[1]
