High-contrast optical bistability using a subwavelength epsilon-near-zero material

Abstract

Optical bistability opens up a promising avenue toward various optical nonlinear functions analogous to their electrical counterparts, such as switches, logic gates, and memory. Free-space bistable devices have unique advantages in large-scale integration. However, most proposed free-space schemes for optical bistability have limitations in one or more aspects of low contrast ratio, compromised compatibility, slow switching speed, and bulk size. Epsilon-near-zero (ENZ) materials have recently shown an ultrafast and giant optical nonlinearity within a subwavelength scale, potentially overcoming these obstacles. Using large-mobility indium-doped cadmium oxide (CdO) as the ENZ material, we numerically demonstrate two efficient schemes for high-contrast optical bistability within a deep subwavelength size based on the ENZ mode and the Berreman mode. The ENZ wavelength can be optically tuned with a typical time scale of sub-picoseconds, giving rise to a switchable bistability between the near-zero state and the high-reflection state. Our work contributes to the advances on compact and ultrafast all-optical signal processing.

New Horizons in Near-Zero Refractive Index Photonics and Hyperbolic Metamaterials

“…The primary question facing the community is whether the benefit of ENZ can overcome its limitations and impact an application of relevance. While recent efforts have suggested avenues in pulse characterization, frequency shifting, ,− bistable devices, , and THz generation, , the work is ongoing. We see potential benefits in areas where control over high irradiances is needed or in scenarios where narrow operating bandwidths are utilized, as well as in the use of weakly resonant structures, such as plasmonic antennas, to provide a middle ground wherein the operational spectral bandwidth can remain reasonably broad (∼100 nm) while gaining additional improvement to the nonlinearity.…”