Double Electromagnetically Induced Transparency and Its Slow Light Application Based On a Guided-Mode Resonance Grating Cascade Structure

Performance analysis of heterostructure-based topological nanophotonic sensor

In this manuscript, a heterostructure-based topological nanophotonic structure is proposed for improved sensing performance. The topological effect is realized by connecting two dissimilar one-dimensional photonic crystal structures having overlapped photonic bandgaps. The structural parameters are optimized to regulate and alter the dispersion characteristics, which results in the opposite Zak phases. This demonstrates a robust topologsical interface state excitation at a 1737 nm operating wavelength. Further, a topological cavity structure having resonance mode at 1659 nm is formed by replacing the interface layers with a defect layer. The mode excitation is confirmed by analyzing the electric field confinement at the interface. The sensing capability of the structure is analytically evaluated by infiltrating different analytes within the cavity. The analytical results demonstrate the device's average sensitivity of around 774 nm/Refractive index unit (RIU) along with an average high Q-factor and figure of merit of around 5.2 × 104 and 2.6234 × 104 RIU-1, respectively. Because of the higher interface mode field confinement, the proposed structure exhibits a 92% higher sensitivity, 98% improved Quality factor, 206% improvement in figure of merit, and 86% higher interface field confinement than conventional Fabry-Perot resonator structures. Thus, the proposed topological cavity structure shows its broad sensing ability (Refractive Index: 1.3-1.6) along with a low-cost, simple fabrication and characterization process, promoting the development of highly sensitive planner nanophotonic devices.

Guiding-mode-assisted double-BICs in an all-dielectric metasurface

The electromagnetically induced transparency (EIT) effect realized in a metasurface is potential for slow light applications for its extreme dispersion variation in the transparency window. Herein, we propose an all-dielectric metasurface to generate a double resonance-trapped quasi bound states in the continuum (BICs) in the form of EIT or Fano resonance through selectively exciting the guiding modes with the grating. The group delay of the EIT is effectively improved up to 2113 ps attributing to the ultrahigh Q-factor resonance carried by the resonance-trapped quasi-BIC. The coupled harmonic oscillator model and a full multipole decomposition are utilized to analyze the physical mechanism of EIT-based quasi-BIC. In addition, the BIC based on Fano and EIT resonance can simultaneously exist at different wavelengths. These findings provide a new feasible platform for slow light devices in the near-infrared region.

Three-level nanogrooves by vibration-assisted fly-cutting for diffraction regulation and array output

Integrating geometric and diffractive optics functions is urgently needed to develop compact equipment for integrating diffraction manipulation and arrayed outputs. In this Letter, a superimposed three-level-grooved surface is proposed to manipulate the diffraction of visible light and provide an array output. Structure design, vibration-assisted fly-cutting, finite-difference time-domain calculations, and diffraction tests are conducted to fabricate the three-level grooves and explore the diffraction mechanism. Nanogrooves with a period close to the middle wavelength of the spectrum primarily enhances the diffraction at low diffraction orders and angles because of resonance. Optical tests prove that these superimposed three-level nanogrooves have a large bandwidth when providing the array output and serving to control and transmit diffracted light. They also show stronger performance for manipulating low diffraction orders.

Multi-Band Analogue Electromagnetically Induced Transparency in DoubleTuned Metamaterials

A multi-band analogue electromagnetically induced transparency (A-EIT) metamaterial is proposed. The structure is composed of liquid crystal (LC) layer and a graphene strips layer on both sides of silicon dioxide. The transmission spectrum and electric field distribution of only one graphene strip and two graphene strips have been studied. As a bright mode, the graphene strip is coupled with adjacent graphene strip to realize the A-EIT effect. When multiple graphene strips are coupled with each other, the multi-band A-EIT is obtained due to the electric dipole resonances of the four strips. The results show that the multiband A-EIT effect can be tuned by voltage on LC and graphene layer, respectively. Moreover, changing the incident angle of the electromagnetic wave has had little influence on the transmission window in the low frequency band, it is meaning that the A-EIT effect with insensitive to the incident angle can be obtained. Each transmission window has a high maximum transmittance and figure of merit (FOM). The multi-band A-EIT effect can widen the application on sensor and optical storage devices.