Abstract
A Bragg-mirror-assisted terahertz (THz) high-contrast and broadband plasmonic interferometer is proposed and theoretically investigated for potential sensing applications. The central microslit couples the incident THz wave into unidirectional surface plasmon polaritons (SPPs) waves travelling to the bilateral Bragg gratings, where they are totally reflected over a wide wavelength range back towards the microslit. The properties of interference between the SPPs waves and transmitted THz wave are highly dependent on the surrounding material, offering a flexible approach for the realization of refractive index (RI) detection. The systematic study reveals that the proposed interferometric sensor possesses wavelength sensitivity as high as 167 μm RIU−1 (RIU: RI unit). More importantly, based on the intensity interrogation method, an ultrahigh Figure-of-Merit (FoM) of 18,750% RIU−1, surpassing that of previous plasmonic sensors, is obtained due to the high-contrast of interference pattern. The results also demonstrated that the proposed sensors are also quite robust against the oblique illumination. It is foreseen the proposed configuration may open up new horizons in developing THz plasmonic sensing platforms and next-generation integrated THz circuits.
Highlights
Over the past several decades we have witnessed a rapidly growing development in the optical sensors for applications of biological and chemical detection [1]
surface plasmon polaritons (SPPs), which are the electromagnetic (EM) waves coupled to electron oscillations and propagating along the interface between a dielectric and a metal, are highly localized in the vicinity of the metal surface, making them extremely sensitive to the variations of the surrounding dielectric environment
The SPPs structures have been widely used in various real-time and label-free sensing applications [6]
Summary
Over the past several decades we have witnessed a rapidly growing development in the optical sensors for applications of biological and chemical detection [1]. The periodic structure-based biosensors can realize the on-chip integration, Nanomaterials 2020, 10, 1385 they suffer from their narrow-band resonant linewidths, or in other words, their sensitivities decrease significantly when the response spectra are away from the resonant wavelengths [26]. To address this spectroscopic issue, we recently proposed and studied several semiconductor-based interferometers based on the waveguide-coupled and slit-groove patterned structures [27,28].
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