Structured electromagnetic fields are central to many advanced optical technologies, including super-resolution microscopy, metrology, trapping, and wavefront shaping. Optical singularities (points, lines, or manifolds where a field property such as phase, polarization, or spin becomes undefined) are a particularly important subset of these structures. Their interest lies not only in the sharp field variations and confinement they generate, but also in the fact that they are often governed by topological and symmetry-based constraints. As a result, they offer both a practical route to enhanced optical functionality and a useful framework for probing fundamental properties of electromagnetic fields.
A canonical example is STED microscopy [1], where a phase singularity produces a donut-shaped depletion beam and allows fluorescence imaging beyond the diffraction limit. More broadly, structured fields containing singular and near-singular features can support localized dark states, steep gradients, and nontrivial spatial correlations, all of which are relevant for sensing and imaging. This motivates the development of platforms that can generate, probe, and control such field structures in a systematic and designable way.
Optical image (left) and SEM images (right) of a metasurface used in [1]. Each of the nanostructures acts as a waveplate, locally controlling both phase and polarization of the transmitted wavefront. Scale bars are 250um and 1um, respectively.
My research focuses on observing, engineering, and controlling electromagnetic fields at the nanoscale, with the goal of accessing structured field configurations that are difficult to realize or study with conventional optical tools. This includes not only the creation of isolated singularities, but also the design of their topology, dimensionality, stability, spatial arrangement, and collective behavior. Nanophotonic systems are particularly attractive in this context because they provide access to subwavelength light structuring and local control over the phase, polarization, and spectral response of optical fields.
Using such platforms, we have experimentally realized new classes of topologically stable optical singularities [1], engineered arrays of dark points for trapping-related applications [2], and, more recently, explored collective effects in singular optics, including superluminal correlations in ensembles of optical phase singularities [4]. Together, these works point toward a broader program in which nanoscale electromagnetic fields are not only observed, but designed and manipulated with increasing precision, enabling new approaches to imaging, sensing, and light–matter control.
Extending the library of optical singularities: Topologically protected, complete polarization singularities. A metasurface can be used to create a topologically protected singularity at the focus of a loosely focusing lens (A). The singularity is a single dark point in space and wavelength (B-C) and its immediate surrounding contains all polarizations (and phases) of light (D). This 'protection shield' makes it stable against perturbations.
Related publications: * denotes equal contribution
[1] Spaegele, C.M., Tamagnone, M., Lim, S.W.D., Ossiander, M., Meretska, M.L. and Capasso, F., 2023. Topologically protected optical polarization singularities in four-dimensional space. Science Advances, 9(24), p.eadh0369. [2] Lim, S.W.D., Park, J.S., Kazakov, D., Spaegele, C.M., Dorrah, A.H., Meretska, M.L. and Capasso, F., 2023. Point singularity array with metasurfaces. Nature Communications, 14(1), p.3237. [3] Lim, S.W.D.* and Spägele, C.M.* and Capasso, F. Topology driven applications in optical singularities. arXiv preprint arXiv:2406.00784. [4] Bucher, T., Gorlach, A., Niedermayr, A., Yan, Q., Nahari, H., Wang, K., Ruimy, R., Adiv, Y., Yannai, M., Lenkiewicz Abudi, T., Janzen, E., Spaegele, C.M., Roques-Carmes, C., Edgar, C., Koppens, F., Vanacore, G., Herzig, H., Sheinfux, Tsesses, S. and Kaminer, I. Superluminal Correlations in Ensembles of Optical Phase Singularities. Nature 651, 920–926 (2026).