Microcavities and nanoresonators are characterized by their quality factors () and mode volumes (). While is unambiguously defined, there are still questions on and, in particular, on its complex-valued character, whose imaginary part is linked to the non-Hermitian nature of open systems. Helped by cavity perturbation theory and near-field experimental data, we clarify the physics captured by the imaginary part of and show how a mapping of the spatial distribution of both the real and imaginary parts can be directly inferred from perturbation measurements. This result shows that the mathematically abstract complex mode , in fact, is directly observable.

The Netherlands Organisation for Scientific Research (NWO)
Resonant Nanophotonics

Cognée, K., Yan, W., La China, F., Balestri, D., Intonti, F., Gurioli, M., … Lalanne, P. (2019). Mapping Complex Mode Volumes with Cavity
Perturbation Theory. Optica, 6(3), 269–273. doi:10.1364/OPTICA.6.000269