Negative refraction in twisted hyperbolic metasurfaces

Hyperbolic metasurfaces with unique dispersion properties can manipulate light–matter interactions according to the demands. However, due to their inherent physical properties, topological transitions (flat bands) exist only in the orthogonal directions, which greatly limit their application. Here, we unveil rich dispersion engineering and topological transitions in hyperbolic metasurfaces. Based on the effective medium theory, the rotation matrix is introduced into the dispersion relation to explain the distorted energy band diagrams, iso-frequency contours and higher-order multi-dipoles of the novel twisted metasurfaces, thereby forming multi-directional topological transitions and surface plasmon polariton propagation. Furthermore, we develop an integrated model to realize new dual-channel negative refraction and nondiffraction negative refraction. The phenomena observed in the experiments match well with the simulations, which proves that the designed metasurfaces make new types of negative refraction possible and will help to overcome the diffraction limit. The hyperbolic metasurfaces presented here exhibit exceptional capabilities for designing microscopes with a super lens at the molecular level, concealment of military aircraft, invisibility cloaks and other photonic devices with higher transmission efficiency.

Multi-wavelength achromatic bifocal metalenses with controllable polarization-dependent functions for switchable focusing intensity

In this paper, bifocal metalens are designed through simultaneously controlling two polarization-dependent functions, which can respectively focus x-polarized and y-polarized light into different positions, and the relative intensity between two foci can be continuously tuned through a simple rotation of the incident linear polarization direction. The proposed metalenses are composed of rectangle nanopillars with spatially varying widths and lengths, which provide distinct propagating phases under two orthogonal polarizations. Therefore, there exists a freedom of degree to achieve two polarization-dependent focusing functions. More importantly, these nanopillars possess the excellent dispersion engineering, and provide an effective way for the realization of achromatic bifocal metalenses. After powerful optimizations, two achromatic bifocal metalenses are constructed and further demonstrated numerically. The x-polarized and y-polarized components are focused into different positions under different working wavelengths. Simulated results agree well with our designs. The approach here is expected to find optical applications in micro-manipulation, optical communication and multicolor display.

Dissipative Kerr solitons at the edge state of the Su-Schrieffer—Heeger model

We investigate analytically and numerically dynamics of dissipative Kerr solitons (DKS) at the edge state of the Su-Schrieffer–Heeger model. We demonstrate that four-wave mixing processes can lead to the formation of DKSs in the edge state of the resonator chain which subsequently initiates photon transfer to the bulk states. We discuss how the edge state soliton can be stabilized by limiting its width within the band gap. Our results contribute to advanced dispersion engineering via mode hybridization in chains of resonators — one of promising ways to achieve broadband frequency combs generation on chip.

Efficient Design for Integrated Photonic Waveguides with Agile Dispersion

Chromatic dispersion engineering of photonic waveguide is of great importance for Photonic Integrated Circuit in broad applications, including on-chip CD compensation, supercontinuum generation, Kerr-comb generation, micro resonator and mode-locked laser. Linear propagation behavior and nonlinear effects of the light wave can be manipulated by engineering CD, in order to manipulate the temporal shape and frequency spectrum. Therefore, agile shapes of dispersion profiles, including typically wideband flat dispersion, are highly desired among various applications. In this study, we demonstrate a novel method for agile dispersion engineering of integrated photonic waveguide. Based on a horizontal double-slot structure, we obtained agile dispersion shapes, including broadband low dispersion, constant dispersion and slope-maintained linear dispersion. The proposed inverse design method is objectively-motivated and automation-supported. Dispersion in the range of 0–1.5 ps/(nm·km) for 861-nm bandwidth has been achieved, which shows superior performance for broadband low dispersion. Numerical simulation of the Kerr frequency comb was carried out utilizing the obtained dispersion shapes and a comb spectrum for 1068-nm bandwidth with a 20-dB power variation was generated. Significant potential for integrated photonic design automation can be expected.

Artificial gauge induced dispersionless coupling for broadband photonic waveguide integration

Coupling among waveguides plays an important role in photonic integration, while it usually suffers from large wavelength dispersion and structural sensitivity that brings difficulties in broadband and robust photonic chip devices. Here, we report a new strategy of dispersion engineering of coupled waveguides by artificial gauge field (AGF) with curved trajectories, which gives rise to a dispersionless broadband coupler function in high-density silicon waveguides (waveguide pitch <λ/2). It is found that the artificial gauge field can generate an inverse dispersion to compensate for the dispersion of conventional waveguide coupling. As such, the coupling between the waveguides can be stable in a broad bandwidth. Based on this design, we demonstrate compact directional and 3dB couplers that show broadband dispersionless coupling of light with wavelength from 1400 to 1650 nm, which also exhibit robustness to considerably large structural variations ~150 nm (75% structural deviation). Furthermore, using the AGF coupler as the building block, we significantly demonstrate a three-level-cascaded waveguide network to route the broadband light to the desired ports, showing a tremendous advantage over the conventional counterparts. Our work exploits the artificial gauge field to integrated photonics and demonstrates the possibility of massive, broadband, robust and dense photonic integrations.