Ricerc@Sapienza

Plasmonic metamaterials and metasurfaces are important for many linear
and nonlinear photonic applications. Here, the possibility to control a nanostructured
layer spontaneously formed near an interface of a thin silver film is
shown, where the interplay between a grain boundary structure and surface
segregation of germanium atoms leads to encapsulation of the grains and,
as the result, formation of a composite metamaterial near the film surface.
This Ag/Ge composite exhibits strong localized surface plasmon resonances

The formation of frequency combs (FCs) in high-Q microresonators with Kerr type of nonlinearity has attracted a lot of attention in the past decade [1]. Recently it has been shown that FCs can be also generated in dissipative dispersive cavities with quadratic nonlinearities [2,3], opening a new possibility of generating combs in previously unattainable spectral regions. Previous work has shown that modulational instability (MI) induces pattern and FC formation in degenerate optical parametric oscillators (OPOs) [4].

Continuously-driven microresonators, whose nonlinear response is dominated by the third-order Kerr nonlinearity, have proven to be valid alternatives to comb sources based on femtosecond mode-locked lasers [1]. More recenlty, the direct generation of optical frequency combs (OFCs) entirely through quadratic interactions has also been demonstrated in singly resonant cavity second harmonic generation (SHG) and in cw pumped nearly degenerate optical parametric oscillation [2,3].

We experimentally demonstrate 2D quadratic extreme events, appearing and disappearing without a trace. Besides the spontaneous formation of self-guided bicolor solitary waves, ultrafast spatial switching, cascaded events and pulse reshaping are observed.