In this work, a dielectric grating/DBR heterostructure has been proposed to create a high-Q hybrid guided mode at nearinfrared (NIR) frequencies. It is found that this nontrivial guided mode can be excited in the dielectric grating/DBR structure, leading to a perfect light transmission with linewidth of about 0.1 nm and Q factor up to 1.3×104. More intriguingly, we show that bound states in the continuum (BIC) can emerge by properly choosing parameters in this resonant regime. The resonant wavelength and Q-factor of this optical mode can be tuned by varying the geometrical parameters, which is polarization-independent under the vertical incident of light. The ultra-narrow linewidth and tunable resonant transmission offered by this simple all-dielectric structure opens new opportunities for developing optical filtering, sensing, and light emitting devices with high-performance.
Particles trapped in optical beams can undergo orbital rotations at the micro/nano-scale and thus find applications in constructing micro-motors/machines, advancing the investigation of micro-rheology, etc. Rather than using the doughnut beams, here we report the orbital rotation of particles in a single Gaussian beam at the wavelength scale. By involving the transverse scattering forces of the light beam in the off-focal plane, the off-axis trapping of nanoparticles is possible and a rotation orbit has been built with small radius even less than the wavelength. Through focusing the incident Gaussian beam with circular polarization, there is the orbital angular momentum converted from the spin angular momentum, and the orbital angular momentum can then drive the particles to undergo orbital rotation. By changing the position of the offfocus plane, the rotation radius and speed can be tuned. The orbital rotation scheme with simple and flexible setup here can find applications in micro-motors and micro-machines.
Here we have investigated the strong coupling of the guided modes with different orders in graphene-based onedimensional (1D) dielectric grating structures in the visible wavelengths. We found that the guided mode resonances (GMR) with different orders can strongly couple with each other under the oblique incidence of light. Absorption spectral response exhibits a distinct spectral anti-crossing with the Rabi splitting up to 59.8 meV. Simulation results further show that the strong coupling of GMR modes enables the bound state in the continuum (BIC) in this coupled system, which can be flexibly modulated by adjusting structural parameters. The proposed hybrid grating structures will benefit the applications in on-chip optical filtering, sensing, and optoelectronic detection.
Here we propose a metasurface consisting of asymmetric dielectric tetramer arrays, which can realize a polarization-sensitive light modulation through toroidal dipole resonance (TDR) in the near-infrared (NIR) region. We found, by breaking the C4v symmetry of the tetramer arrays, two narrow-band TDRs can be created with the linewidth around 1.5 nm. Multipolar decomposition of scattering power and electromagnetic field distribution calculations confirm the excitation of TDRs. Our simulation results show that 100% modulation depth in light absorption and selective field confinement can be achieved by changing the polarization orientation of the incident light. Our findings will prompt versatile applications in optical switching, storage, polarization detection, and light emitting devices.
Strong and narrow-linewidth circular dichroism (CD) spectroscopy promises potential applications in bio-chemical sensing and detection of the weak chirality in natural molecules. Here we proposed a chiral metasurface formed by the asymmetric metal double split ring resonator (DSRR) arrays, the circular dichroism (CD) of which has been investigated. The maximum CD for absorption response of the metasurface can reach 0.61 with an ultra-narrow spectral linewidth of 9.6 nm in the mid-infrared (MIR) band. Our calculation results show that the chiral metasurface can support two surface lattice resonance modes for the left circularly polarized (LCP) and right circularly polarized (RCP) light. The narrow linewidth of CD is enabled by the spin-selective high-Q resonance modes with a differential absorptivity for LCP and RCP light. Our findings shed light on the potential applications in spin-selective perfect optical absorption, high-sensitive polarization detection, and chirality sensing.
We have theoretically studied the strong coupling of the surface plasmon polaritons (SPP) and magnetic polaritons (MP) modes in an Au grating/dielectric/Au resonance structure in the near-infrared waveband. Our results show that SPP and MP modes can strongly interact with each other at the metal grating/dielectric/metal (MDM) interface, leading to a large Rabi splitting. We also find that the light absorptivity in the high- and low-frequency branches within the anticrossing region are abnormally different. Moreover, the simulation results indicate that strong SPP-MP coupling can be tuned by modulating the geometric parameters of the structure. The unique characteristics of strong coupling of SPP and MP modes in this simple MDM hybrid structure will be helpful in the design of various polaritonic devices.
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