Controlling the Speed of an All Optical Switch by Combining Fast and Slow Materials*

All-optical switches control the amplitude, phase, or polarization of light at ultrafast timescales utilizing optical pulses. They operate without the delays of electronic circuits, giving them upto terahertz speeds, and making them essential for both applications like data processing and for fundamental science experiments such as frequency translation or photonic time crystal design. This makes it necessary to understand the role of light-matter interactions on the dynamic optical response of such systems. 

In this work, we combine fast and slow materials to achieve control over the zero to zero response of an all-optical switch. We design a metasurface combining titanium nitride (TiN) and aluminum-doped zinc oxide (AZO) on the same platform. The metasurface supports two Berreman modes, one near the epsilon-near-zero point of titanium nitride, and another near that of AZO. TiN has a nanosecond lattice cooling time, whereas AZO has a picosecond optical response.

When probed near the ENZ point of titanium nitride, the metasurface exhibits a slow, nanosecond-scale response. When probed near the ENZ of the faster material (AZO), it exhibits an ultrafast, picosecond response. At wavelengths between the resonances, the dynamics of the metasurface can be modeled by a weighted summation of the response of the two materials. Thus, the same metasurface shows variable zero-to-zero response times that span the picosecond scale to the nanosecond scale.

We show that the response time of an all-optical switch can be controlled by combining fast and slow nonlinearities in different materials. This method adds an extra degree of freedom for controlling the speed of an all-optical switch, by controlling the constituent materials and the wavelength of operation. A comprehensive understanding of the temporal response of materials will enable us to design better nonlinear optical devices and experiments spanning the telecom to the mid-infrared regime.