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The effect of different geometric parameters on the reflection spectrum.

In this paper, we propose and demonstrate a dual-channel self-calibration multimode optical-fiber surface plasmon resonance thermometer. The structure of this thermometer is mainly composed by dual sensing channels, in which one channel is coated with a gold layer surrounded by liquid crystal (LC), and the other is prepared with bilayers of silver and thin indium tin oxide (ITO) layer. The gold channel is the main channel, and the channel of the ITO layer with high refractive index is viewed as a configuration of self-calibration. The experimental results of the system show that the temperature sensitivities are 1.006 nm/°C in the range of 20°C–34°C and 0.058 nm/°C in the range of 35°C–80°C. In particular, at the phase transition temperature 34.5°C of changing from the nematic to the isotropic phase of the LC, the temperature sensitivity shows a step increase of 6.8 nm with a unit temperature change. This structure can be highly advantageous for temperature controlling and alarming in laboratory monitoring and industrial production.

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.

Nanostructures, supporting hybrid plasmonic–photonic modes that combine the advantages of the electromagnetic field enhancement of the localized plasmon resonances (LSPRs) and the higher quality factor of the photonic resonances, have served as flexible and efficient platforms for engineering strong light–matter interactions. Here, we demonstrate theoretically that the two-dimensional metallic photonic crystals (PhCs) as a class of hybrid plasmonic–photonic lattices play an active role in light–matter interaction. The metallic PhCs are composed of optical waveguides strongly coupled to periodically arranged metallic nanodisks, and this coupling gives rise to the formation of waveguide–plasmon polaritons. By combining two-dimensional semiconducting materials (WS2) and the metallic PhCs, we prove strong coupling between waveguide–plasmon modes and excitons at room temperature. The strong coupling includes three types of resonances: guided modes excited by diffractive gratings, LSPRs on individual nanodisks, and WS2 excitons. Using coupled oscillator models, we show that the mode composition and coupling strength between polaritons can be controlled effectively by tuning the geometrical factor of the lattice, and thus reveal the LSPR-mediated energy transfer process. Our reports are not only of fundamental interest but could also be useful for practical applications based on monolayer semiconductors.

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.