Broadband and Ultra-Low Threshold Optical Bistability in Guided-Mode Resonance Grating Nanostructures of Quasi-Bound States in the Continuum

Nonlinear optical bistability based on epsilon-near-zero mode in near-infrared band

We propose a simple thin-layer structure based on epsilon-near-zero mode field enhancement to achieve optical bistability in the near-infrared band. The high transmittance provided by the thin-layer structure and the electric field energy limited in the ultra-thin epsilon-near-zero material means that the interaction between the input light and the epsilon-near-zero material can be greatly enhanced, creating favorable conditions for the realization of optical bistability in near-infrared band. The optical bistability hysteresis curve is closely related to the incident angle of light and the thickness of epsilon-near-zero material. This structure is relatively simple and easy to prepare, so we believe that this scheme will have a positive effect on the practicality of optical bistability devices in all-optical devices and networks.

Ultralow-level all-optical self-switching in a nanostructured moiré superlattice

We report an all-optical self-switching performed at an ultralow-level of intensity in a nanostructured moiré superlattice on a silicon platform. The moiré superlattice was formed by twisting two sets of triangular lattices in a silicon membrane in the same layer with a twist angle of 9.43°. The near flatband was formed, and the electric field was well confined in the center of the superlattice, which enabled all-optical switching under an ultralow intensity when the Kerr nonlinearity of silicon was considered. The intensity, which was reduced to 300 W/m² and even 20 W/m², can cause the transmittance of the nanostructure to change from 0 to 80% under x- and y-polarized pump light, respectively, and could be further decreased by optimizing the nanostructure or nonlinear materials. The results indicate that moiré superlattices fabricated from nonlinear materials are promising for integrated all-optical devices.

Temperature controllable Goos-Hänchen shift and high reflectance of monolayer graphene induced by BK7 glass grating

BK7 glass has an unusual temperature-dependent refractive index and thickness, which provides a promising platform for uncovering the temperature-related optical phenomena and applications. Here, we theoretically demonstrate that monolayer graphene based BK7 glass grating structure has two Goos-Hänchen (GH) peaks with respective magnitudes of2564λand1993λ,and their corresponding reflectances are also high. The electromagnetic field distribution in this structure directly reveals that the enhanced GH shifts can be ascribed to the excitation of the guide mode resonances in the waveguide dielectric layer below BK7 glass grating structure and their high reflectances are granted by the constructive interferences between the reflected waves. In addition, the magnitudes of the GH peaks can be controlled by the temperature of BK7 glass as well as the chemical potential of monolayer graphene. We also evaluate the temperature sensing property of this structure based on the GH shifts and find that its maximum temperature sensitivity can be up to5.0017×104μm°C-1.The enhanced and controlled GH shift presented in monolayer graphene based BK7 glass grating structure shows promise for the applications, such as, optical sensors, temperature sensors, and optoelectronic detectors.

Evolution of optical harmonic generation near bound-states in the continuum in hybrid plasmonic-photonic structures

We investigate the nonlinear optical harmonic generation behaviors near the bound-states in the continuum (BICs) in hybrid plasmonic-photonic structures. The hybrid structures are designed to consist of a plasmonic grating covered with a nonlinear dielectric waveguide layer, which support two distinct groups of BICs, i.e. the symmetry-protected BICs and Friedrich-Wintgen BICs. The evolution of second- and third-harmonic generation (SHG and THG) near the two groups of BICs was studied. The high dependence of nonlinear response on the local field distribution and tensor components of susceptibility of nonlinear materials was determined. Especially, there exists optimized angles of incidence for efficient SHG and THG response due to the interaction of photonic and plasmonic modes. The results are important to understand the nonlinear response behaviors in hybrid plasmonic-photonic structures and to design the nonlinear photonic devices.