Thomas Pertsch

Hybrid photonic nanomaterials for nanoscale nonlinear interactions (Conference Presentation)

Photonics nanomaterials are considered to be a major source of innovation for advanced optical systems, since their electromagnetic properties can be engineered by implementing a suitable geometry of their nano-sized elementary unit cells. While for many applications mainly their far field properties, i.e. the influence on the reflected, transmitted, and scattered fields measurable in a distance large compared to the exciting wavelength, are of interest, they provide many degrees of freedom to influence also the nearfields surrounding the unit cells. This becomes important particularly if nonlinear light matter interaction is exploited, where the far field response depends critically on the local field strength. Hence nanomaterials offer a conceptually new way to tailor the nonlinear material properties to the needs of particular applications. Furthermore new types of nonlinearities, by e.g. surface effects, become important, due to the increased surface to volume ratio of nanomaterials.nIn this presentation we will present our recent results on nonlinear optical investigations of photonic nanomaterials, which derive from the hybridization of resonant photonic nanostructures, which provide highly dispersive field enhancement. The hybridization of such metallic or dielectric nanoresonators with highly nonlinear materials, as e.g. atomically thin semiconducting membranes, classical semiconductors, or ferroelectrics, provides a route towards even more efficient nonlinear processes. Furthermore we will show examples of how the combined control of dispersive and nonlinear properties can be exploited to address applications in frequency conversion, quantum light sources and sensing.

Disordered photonic metasurfaces for complex light field control (Conference Presentation)

Optical metasurface can provide control over wavefront, polarization and spectrum of light fields while having just nanoscale thickness, making them promising candidates for flat optical components. Most metasurfaces studied so far consist of two-dimensional subwavelength arrays of designed metallic or dielectric scatterers. Deviations from a periodic, ordered arrangement are usually associated with a deterioration of the optical properties. However, the introduction of controlled disorder also provides interesting opportunities to engineer the optical response of metasurfaces. For example, the introduction of disorder can decrease unwanted anisotropy in the optical response [1], it suppresses scattering into discrete diffraction orders, and it can enhance the metasurfaces’ channel capacity [2].nHere we investigate different types of disordered metasurfaces. We demonstrate that the introduction of rotational disorder at the unit-cell level enables the realization of chiral plasmonic metasurfaces supporting pure circular dichroism and circular birefringence. We show experimentally that the polarization eigenstates of these metasurfaces, which coincide with the fundamental right- and left-handed circular polarizations, do not depend on the wavelength over the spectral range of the metasurface resonances. Thereby, our metasurfaces mimic the behaviour of natural chiral media, while providing a stronger chiral response. Furthermore, we systematically investigate how the introduction of different types of positional disorder influences the complex transmittance spectra of Mie-resonant silicon metasurfaces, showing that disorder provides an independent degree of freedom for engineering their spatial and spectral dispersion. n[1] S. S. Kruk et al., Phys. Rev. B 88, 201404(R) (2013).n[2] D. Veksler et al., ACS Photonics 2, 661 (2015).

Holographic progressive lenses

Progressive addition lenses (PALs) are realized as optical freeform surfaces by complex manufacturing and inspection processes. In turn, holographic optical elements (HOEs) enable fast and easy fabrication in other applications. Here we present a design method for the combination of both; HOEs that are designed to fulfill the optical function of PALs. We describe how inherent limitations of HOEs, such as angular and wavelength selectivity as well as grating dispersion can be overcome. We show that holographic PALs can be optimized to have a distribution of spherical power and astigmatism, which is a qualitative replication of the performance of their refractive counterparts. The design rules we identify are shown for PALs but have the potential to improve other applications of HOEs as well.

High Effciency Harmonic Generation in LiNbO 3 Membranes

We reveal simultaneous phase- and group-velocity matching for frequency doubling of ultra-short pulses at telecom wavelengths in LiNbO3membranes. Furthermore, we predict complete phase-matched cascaded third-harmonic generation for optimized membrane thickness.

Angle-Independent Bistability in an All-Photonic-Crystal Fabry-Pérot Resonator

We find an almost angle-independent bistability of the cavity field in dependence on the pump for an all-photonic crystal Fabry-Perot resonator operating in the subdiffractive regime. Finite-difference time-domain calculations are used to obtain the hysteresis.

Radiation Losses of Photonic Crystal Waveguides in LiNbO 3 Membranes

The impact of the air gap separating a photonic-crystal membrane from the underlying substrate on radiation losses is investigated. The proposed photonic-crystal geometry can be fabricated by means of ion-beam enhanced etching.