Nonlinear photonic nanostructures that allow efficient all-optical switching are considered to be a prospective platform for novel building blocks in photonics. We performed time-resolved measurements of the photoinduced transient third-order nonlinear optical response of a fishnet metamaterial. The mutual influence of two non-collinear pulses exciting the magnetic resonance of the metamaterial was probed by detecting the third-harmonic radiation as a function of the time delay between pulses. Subpicosecond-scale dynamics of the metamaterial’s χ(3) was observed; the all-optical χ(3) modulation depth was found to be approximately 70% at a pump fluence of only 20 μJ/cm2.
Nonlinear metasurfaces have become prominent tools for controlling and engineering light at the nanoscale. Usually, the polarization of the total generated third harmonic is studied. However, diffraction orders may present different polarizations. Here, we design an high quality factor silicon metasurface for third harmonic generation and perform back focal plane imaging of the diffraction orders, which present a rich variety of polarization states. Our results demonstrate the possibility of tailoring the polarization of the generated nonlinear diffraction orders paving the way to a higher degree of wavefront control.
Metasurfaces
are versatile tools for manipulating light; however,
they have received little attention as devices for the efficient control
of nonlinearly diffracted light. Here, we demonstrate nonlinear wavefront
control through third-harmonic generation (THG) beaming into diffraction
orders with efficiency tuned by excitation of hybrid Mie–quasi-bound
states in the continuum (BIC) modes in a silicon metasurface. Simultaneous
excitation of the high-Q collective Mie-type modes and quasi-BIC modes
leads to their hybridization and results in a local electric field
redistribution. We probe the hybrid mode by measuring far-field patterns
of THG and observe the strong switching between (0,–1) and
(−1,0) THG diffraction orders from 1:6 for off-resonant excitation
to 129:1 for the hybrid mode excitation, showing tremendous contrast
in controlling the nonlinear diffraction patterns. Our results pave
the way to the realization of metasurfaces for novel light sources,
telecommunications, and quantum photonics.
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.
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