High-Performance Quality Factor Based Sensor With Diagonal Cylinder Metasurface of the Bound State in the Continuum

High-quality-factor(high-Q-factor)electromagnetic resonance plays an important role in sensor applications.Previously proposed gas refractive index sensors are often limited by the large cavity length or microscale fabrication process in practical applications.Recently,ultra-high Q factor resonance based on the bound state in the continuum(BIC)has provided a feasible approach to solve these problems.In this paper,we propose a metasurface structure consisting of a single size tetramer cylinder.It supports dual band toroidal dipole(TD)resonances driven by BIC.The physical mechanism of double TD resonances is clarified by the multipole decomposition of the metasurface band structure and far-field scattering power.The sensor structure based on this achieves a sensitivity of 518.3 MHz/RIU,and the maximum line width does not exceed 680kHz.The high-Q-factor electromagnetic resonance has the advantages of polarization independence and simplicity to manufacture.These findings will open up an avenue to develop the ultrasensitive sensor in the gigahertz regime.

Bessel–Gauss photon beams with fractional order vortex propagation in weak non-Kolmogorov turbulence

We model the effects of weak fluctuations on the probability densities and normalized powers of vortex models for the Bessel–Gauss photon beam with fractional topological charge in the paraxial non-Kolmogorov turbulence channel. We find that probability density of signal vortex models is a function of deviation from the center of the photon beam, and the farther away from the beam center it is, the smaller the probability density is. For fractional topological charge, the average probability densities of signal/crosstalk vortex modes oscillate along the beam radius except the half-integer order. As the beam waist of the photon source grows, the average probability density of signal and crosstalk vortex modes grow together. Moreover, the peak of the average probability density of crosstalk vortex modes shifts outward from the beam center as the beam waist gets larger. The results also show that the smaller index of non-Kolmogorov turbulence and the smaller generalized refractive-index structure parameter may lead to the higher average probability densities of signal vortex modes and lower average probability densities of crosstalk vortex modes. Lower-coherence radius or beam waist can give rise to less reduction of the normalized powers of the signal vortex modes, which is opposite to the normalized powers of crosstalk vortex modes.

Plasmonic sensor with variable claddings based on metallic slit arrays

We propose a plasmonic sensor with variable refractive index(RI),which exhibits high sensitivity and extraordinary optical transmission(EOT).Its variable RI is attributed to its dielectric layers and metallic slit arrays.According to simulation results,the third resonant wavelength has a wavelength sensitivity of 800 nm/RIU and an ultra-high transmittance of 0.8 by adjusting the RIs of the upper and lower dielectrics,incident light angle,and structural geometric parameters.With its unique features,the proposed structure holds considerable potential for extensive application to metal–dielectric grating sensors operating at visible and near-infrared frequencies.