Ultrafast all-optical diffraction switching using semiconductor metasurfaces

Ultrafast all-optical switching using Mie resonant metasurfaces requires both on-demand tunability of the wavefront of the light and ultrafast time response. However, devising a switching mechanism that has a high contrast between its on and off states without compromising speed is challenging. Here, we report the design of a tunable Mie resonant metasurface that achieves this behavior. Our approach utilizes a diffractive array of semiconductor resonators that support both dipolar and quadrupolar Mie resonances. By balancing the strengths of the dipole and quadrupole resonances, we can suppress radiation into the first diffraction order, thus creating a clearly delineated off-state at the operating wavelength. Then, we use optical injection of free- carriers to spectrally shift the multipoles and rebalance the multipole strengths, thereby enabling radiation into the diffraction order-all on an ultrafast timescale. We demonstrate ultrafast off-to-on switching with I-on/I-off approximate to 5 modulation of the diffracted intensity and ultrafast on-to-off switching with I-on/I-off approximate to 9 modulation. Both switches exhibit a fast tau(tr)approximate to 2.7 ps relaxation time at 215 mu J cm(-2) pump fluence. Further, we show that for higher fluences, the temporal response of the metasurface is governed by thermo-optic effects. This combination of multipole engineering with lattice diffraction opens design pathways for tunable metasurface-based integrated devices.

Automated summary

In this study, a tunable Mie resonant metasurface based on a diffractive array of semiconductor resonators was designed for ultrafast all-optical switching. By balancing dipolar and quadrupolar Mie resonances, the metasurface can achieve radiation into different diffraction orders and demonstrate fast switch responses. The metasurface's temporal response is governed by thermo-optic effects at higher pump fluences.