Resonant Phase

Resonant phase is the phase shift that occurs when the incident light couples strongly to a resonant mode of a subwavelength meta-atom. Near resonance, the scattering and transmission of the nanostructure are strongly modified, and the phase of the transmitted field can vary rapidly with frequency or geometry. This rapid variation is exactly what makes resonant meta-atoms valuable in flat optics.

A resonant meta-atom behaves somewhat like a tiny optical cavity. The electromagnetic field is confined near or inside the structure, and the field distribution changes in a way that strongly influences the phase of the outgoing wave. As the geometry is tuned, the resonance shifts, and the transmitted phase can sweep through a large range—often nearly the full $2\pi$ span needed for a lens phase profile.

The resonance may be of several types. In dielectric nanostructures, Mie resonances are common, while in some multilayer or hybrid systems one also sees Fabry–Pérot-like resonances. These resonances provide a way to obtain strong phase modulation without requiring a large thickness. This is one reason metalens design often relies on carefully engineered resonant nanostructures.

The tradeoff is that resonant phase control is often more sensitive to wavelength, polarization, and fabrication tolerances. In exchange, it offers strong local phase tunability and efficient optical response in compact devices. This makes resonant approaches particularly useful for wavelength-specific applications and high-performance metasurface design.

Key features

Strong field confinement near resonance.
Rapid phase change as a function of wavelength or geometry.
Full or nearly full phase coverage across a designed range.
Useful for compact, sharp optical phase steering.

Resonant phase uses the response of a nanostructure near its electromagnetic resonance to achieve large and rapid phase modulation.

References

[1] Decker, M., Staude, I., Falkner, M., Dominguez, J., Neshev, D. N., Brener, I., Pertsch, T., & Kivshar, Y. S. (2015). High-efficiency dielectric metasurfaces performing operations with magnetic and electric resonances. Advanced Optical Materials, 3(6), 813–820. https://onlinelibrary.wiley.com/doi/10.1002/adom.201400584

[2] Kuznetsov, A. I., Miroshnichenko, A. E., Brongersma, M. L., Kivshar, Y. S., & Luk’yanchuk, B. (2016). Optically resonant dielectric nanostructures. Science, 354(6314), aag2472. https://www.science.org/doi/10.1126/science.aag2472

[3] Wikipedia contributors. “Mie theory.” https://en.wikipedia.org/wiki/Mie_theory