We present a plasmonic all-optical switch based on Mach-Zehnder interferometer (MZI) with local nonlinearity. The design of the miniaturized all-optical switch is possible by employing surface-plasmon polaritons (SPPs) that confine the energy of electromagnetic (EM) waves at sub-wavelength scale. The coupling between sub-wavelength plasmonic waveguides in MZI and a control beam generates 'ON' and 'OFF' states at the switch and switching between 'ON' and 'OFF' states happens when the control beam is turned on or off. The waveguides cladding in the switch structure is made of lossy media including metamaterials with positive and negative EM susceptibilities and metals; the core consists of nonlinear and dielectric media. Employing materials with negative EM susceptibilities in the switch structure facilitates the propagation of both transverse electric and transverse magnetic SPPs along the waveguides. Our all-optical switch design enables multi-frequency switching with low-intensity control field. Ascertaining the capabilities of multi-frequency plasmonic all-optical switches facilities their applications in miniaturized photonic circuits and in biosensors.

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We demonstrate a novel, label-free and real-time tunable infrared biosensor by employing surface-plasmon polaritons in asymmetric Mach-Zehnder interferometer. The waveguides cladding in the Mach-Zehnder interferometer is made of lossy media with positive and negative electromagnetic susceptibilities, including metamaterial, metal and graphene. The core consists of dielectric media. We introduce two configurations for our biosensor structure. First configuration is an open-path structure and the second one consists of a sample housing made of a silicon layer around the structure. We also present a tunable biosensor by applying a gate voltage to the graphene in the structure. We employ three different cancerous cells, including cervical, breast and basal, as samples to examine the capabilities of the biosensor. Our biosensor structure is highly sensitive, compared to the existing biosensors in the literature, with the sensitivity for basal cancer cell of 1034THz/RIU. The proposed biosensor structure is compact and easy to fabricate with applications in biomedical sensing and environmental control to detect water pollutants.