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A plasmonic splitter based on slot cavity is proposed and numerically investigated using finite-difference-time-domain (FDTD) methods. The structure consists of the input waveguide, a slot cavity and output waveguides. By varying positions of output waveguides, frequency splitter and power splitter can be achieved in the proposed structure. Flexible output power ratio is feasible through further adjusting the coupling distance and the refractive index of output waveguides.

In this paper, a multichannel refractive index sensor based on a subwavelength metal–insulator–metal (MIM) waveguide coupled with tangent-ring resonators is proposed. When two tangent-ring resonators were placed above the MIM waveguide, Fano resonance with asymmetrical line shape appeared in the transmission spectrum due to the interference between the light–dark resonant modes. The sensitivity and figure of merit were as high as 880 nm/RIU and 964, respectively. Through adding more tangent-ring resonators, multiple Fano resonances with ultrasharp peaks/dips were achieved in the wavelength range of 800–2000 nm. Besides, negative group delays were also observed in the Fano resonant dips. Two-dimensional finite-difference time-domain (FDTD) method was used to simulate and analyze the performances of the proposed structures. These kinds of multiring structures can find important applications in the on-chip optical sensing and optical communication areas.

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A plasmonic metal-dielectric-metal (MDM) waveguide structure is proposed by placing a slot cavity below or above a groove. The groove and the slot cavity can act as a reflector and a resonator, respectively. Due to the interactions between the broad dark mode and the narrow bright mode caused by the groove and the side-coupled slot cavity, single Fano resonance with sharp asymmetric spectral profile is achieved. Interestingly, dual Fano resonances can also be obtained by using two different slot cavities, which are simultaneously distributed on both sides of the groove. The line shape can be transformed by changing the length of the groove, while the wavelength of the resonance peak can be manipulated linearly with the length of the slot cavity. The proposed structure yields a highest sensitivity of ∼1131 nm/RIU and a figure of merit of ∼1.6×10 7 , and thus, we believe that it can serve as an on-chip nanosensor.

High-speed railway systems have begun to be widely deployed. To meet increasingly stringent requirements under harsh running environments, we propose and demonstrate three fiber-Bragg-grating (FBG)-based approaches for the strain measurement and axle counting in high-speed railway systems, including matched gratings, grating under uneven strain distribution, and semi-free grating. All approaches are laboratory verified and evaluated using the train load platform. Pros and cons are also discussed in terms of feasibility and cost-effectiveness.

We investigate a plasmonic waveguide system based on side-coupled complementary split-ring resonators (CSRR), which exhibits electromagnetically induced transparency (EIT)-like transmission. LC resonance model is utilized to explain the electromagnetic responses of CSRR, which is verified by simulation results of finite difference time domain method. The electromagnetic responses of CSRR can be flexible handled by changing the asymmetry degree of the structure and the width of the metallic baffles. Cascaded CSRRs also have been studied to obtain EIT-like transmission at visible and near-infrared region, simultaneously.

A plasmonic multi-channel filter with individual export for each transmission peak is proposed on the basis of a metal–insulator–metal (MIM) structure. There are a series of slot cavities arrayed on both sides of the MIM slit. Surface plasmon polaritons (SPPs) are captured into the cavities resulting in multiple resonance modes. By choosing the proper positions for the drop waveguides, the first and the second resonance wavelengths can be coupled out from the corresponding exports, respectively. The central transmission-peak wavelengths can be modified by the variation of the length of the slot cavities. For a single export, there is only one peak in a large wavelength range. Two-, four-, and eight-channel filters have been designed and numerically demonstrated by the 2D finite difference time-domain method. This proposed scheme can be used in wavelength demultiplexing and fluorescence spectroscopy areas.