Magneto-plasmonic sensors based on surface plasmon resonance have been studied considerably in recent years, as they feature high sensitivity and ultrahigh resolution. However, the majority of such investigations focus on prism-based sandwich architectures that not only impede the miniaturization of devices but also have a weak transverse magneto-optical Kerr effect (TMOKE) in magnitude. Herein, we theoretically demonstrate a magneto-plasmonic sensor composed of Au/Co bilayer nanodisk arrays on top of optically thick metallic films, which supports a narrow surface plasmon resonance (SPR) with a bandwidth of 7 nm and allows for refractive index sensitivities as high as 717 nm/RIU. Thanks to the high-quality SPR mode, a Fano-like TMOKE spectrum with a subnanometer bandwidth can be achieved in the proposed structure, thereby giving rise to ultrahigh sensing of merit values as large as 7000 in water. Moreover, we demonstrate a large TMOKE magnitude that exceeds 0.6. The value is 1 order of magnitude larger than that of magneto-plasmonic sensors reported. We also demonstrate that the behavior of TMOKE spectra can be controlled by tuning the geometrical parameters of the device including the diameter and thickness of nanodisk arrays. This work provides a promising route for designing magneto-plasmonic sensors based on metasurfaces or metamaterials.

Nanostructures with combined magnetic and plasmonic properties have become an active subject of research in recent years. However, most of magneto-plasmonic systems as biosensors adopt a complex intertwined configuration or operate in the monochrome excitation. In this work, we present a simple magneto-plasmonic system which consists of an Au nanowire array on top of a cobalt film, and theoretically demonstrate an enhanced transverse magneto-optical Kerr effect (TMOKE) of the system under the excitation of broadband light source. We study the tunable mechanism of the structure and also expound the correlation of the magnitude of the magneto-optical effect and the contrast ratio of reflection spectra, demonstrating that the high spectral contrast ratio is favorable for obtaining a giant TMOKE value with a sharp Fano-like resonance. In addition, the electromagnetic fields are strongly enhanced in the system due to the introduction of the Co layer, giving rise to high bulk sensitivities as large as 693 nm RIU −1 in a wide refractive index range of 1.00-1.40. With the TMOKE measurements, we demonstrate huge values of the sensing figure of merit as large as 4192 in a saline environment.

Optical cavities supporting the optical bound states in the continuum (BICs) with infinite radiative lifetime have recently been widely reported. Here, we theoretically investigate BICs in an ultrathin photonic structure consisting of a multilayer, nanostructured transition metal dichalcogenide (TMD). Using finite element simulations, we demonstrate two distinct groups of BICs, namely symmetry-protected BICs and interference-based BICs, in the photonic system. Under normal incidence, their dispersion can be mediated by altering the grating pitch, which makes it possible to explore the strong coupling of these two photonic modes with the TMD exciton band in the same structure. This work expands not only the library of traditional nanophotonic approaches, but also provides more possibilities for optoelectronic devices toward miniaturization.

In this paper, we introduce a novel method for the fabrication of self-assembly plasmonic metamaterials by exploiting fluid instabilities of optical thin films. Due to interplay between template reflow and spinodal dewetting, two metal nanoparticles of different sizes are generated on the top mesas of free-standing porous anodic aluminum oxide (AAO) template, which results in the apprearance of double resonant peaks in the extinction spectrum. These two resonant peaks possess refractive index resolution 3.27 × 10−4 and 2.53 × 10−4 RIU, respectively. This optical intensity modulation based plasmonic nanoplatform shows a dramatically surface sensing performance with outstanding detection capacity of biomolecules, because of the very small decay length of electric field at dual-modes. The detection ability for concanavalin A (Con A) demonstrats that the limit of detection of dual-modes reaches as small as 68 and 79 nM, respectively.

Resonant dielectric metasurfaces have been demonstrated to hold a great promise for manipulation of light-wave dispersion at the nanoscale due to their resonant photonic environment and high refractive index. However, the efficiency of devices based on dielectric nanostructures is usually limited by the quality (Q) factor of their resonant modes. The physics of the bound sates in the continuum (BICs) provide an elegant solution for control over the Q factor of resonant modes. Here, by engineering the substrate of Si-based metasurfaces, we demonstrate two eigenmodes that exhibit an intrinsic magnetic dipole character and have an infinite radiation lifetime. We reveal that they are characterized by in-plane and out-of-plane magnetic dipole modes and respectively correspond to two groups of BICs, that is, Fabry–Pérot BICs and symmetry-protected BICs. Using temporal coupled-mode theory and numerical simulations, we show that these BIC modes can transform into high-Q quasi-BIC resonances with near-unity absorption under normal incidence through tuning structural parameters. Our work provides a promising route to use BIC-inspired metasurfaces for designing ultra-narrowband absorbers which can be used as absorption filters, photodetectors, and sensors.