Highly resonant photonic structures, such as cavities and metasurfaces, can dramatically enhance the efficiency of nonlinear processes by utilizing strong optical field enhancement at the resonance. The latter, however, comes at the expense of the bandwidth. Here, we overcome such tradeoff by utilizing time-varying resonant structures. Using harmonics generation as an example, we show that the amplitude and phase format of the excitation, as well as the time evolution of the resonator, can be optimized to yield the strongest nonlinear response. We find the conditions for an efficient synthesis of electromagnetic signals that surpass the cavity bandwidth, and discuss a potential experimental realization of this concept.

Localized electromagnetic modes and negligible Ohmic losses dictate the growing interest to subwavelength all-dielectric nanoparticles. Although an exhaustive volume of literature dealt with interaction of all-dielectric nanostructures with free-space electromagnetic fields, they received little attention as integrated photonic elements. We present an experimental and numerical study of optical coupling between a resonant subwavelength silicon nanodisk and a silicon nanowire, as probed by third harmonic generation microscopy and full-wave simulations. First, by placing the nanodisks at different distances from the nanowire, we observed third harmonic intensity modulation by a factor of up to 4.5. This modulation is assigned to changes in the local field enhancement within the nanodisks caused by their coupling to the nanowires and subsequent shifting and broadening of their magnetic-type resonances. Interestingly, although the nanowire presents an additional loss channel for the nanodisk, we observed an increase in the local field strength within the nanodisk, as verified by rigorous full-wave simulations. Inversely, for the gap sizes that are smaller than ≈200 nm, we observe the influence of the nanoparticles on the propagation properties of the fundamental waveguide modes of the nanowire. The better understanding of the mutual influence of the Mie-resonant nanoparticles and waveguiding structures heralds integration of the former on-photonic chips.

Resonant photonic nanostructures exhibiting enhanced nonlinear response and efficient frequency conversion are an emergent platform in nonlinear optics. High-index semiconductor metasurfaces with rapidly tuned high-quality-factor (high-Q) resonances enable a novel class of timevariant metasurfaces, which expands the toolbox of color management at the nanoscale. Here, we report on the dynamic control of the nonlinear optical response in time-variant semiconductor metasurfaces supporting high-Q resonances in the near-infrared spectral range. Germanium metasurfaces reveal frequency conversion of the fundamental beam and blue-shift of 10 nm (3.05ω) and 40% broadening in the third-harmonic spectrum due to a subpicosecond-scale time-variant refractive index. A time-dependent coupled-mode theory, in qualitative agreement with the experimental data, validated the time-variant nature of the system. Our findings expand the scope of time-variant metasurfaces and may serve as base for the next generation of nanoscale pulse shapers, optical switches, and light sources.

Localized electromagnetic modes and negligible Ohmic losses dictate the growing interest in subwavelength all-dielectric nanoparticles. Although an exhaustive volume of study dealt with interaction of all-dielectric nanostructures with free-space electromagnetic fields, their performance as integrated photonics elements remains untackled. We present an experimental study of optical coupling between a resonant subwavelength silicon nanodisk and a non-resonant silicon waveguide, as probed by third harmonic generation microscopy. By placing the nanodisks at different distances from the waveguide, we observe third harmonic intensity modulation by a factor of up to 4.5. This modulation is assigned to changes in the local field enhancement within the nanodisks caused by their coupling to the waveguides and subsequent modulation of their magnetic-type resonances. Interestingly, although the waveguide presents an additional loss channel for the nanodisk, we observe an increase in the local field strength within the nanodisk, as verified by rigorous full-wave simulations. This work makes a step toward integration of all-dielectric nanoparticles on photonic chips.