Seeking better surface plasmon polariton (SPP) waveguides is of critical importance to construct the frequency-agile terahertz (THz) front-end circuits. We propose and investigate here a new class of semiconductor-based slot plasmonic waveguides for subwavelength THz transport. Optimizations of the key geometrical parameters demonstrate its better guiding properties for simultaneous realization of long propagation lengths (up to several millimeters) and ultra-tight mode confinement (~λ2/530) in the THz spectral range. The feasibility of the waveguide for compact THz components is also studied to lay the foundations for its practical implementations. Importantly, the waveguide is compatible with the current complementary metal-oxide-semiconductor (CMOS) fabrication technique. We believe the proposed waveguide configuration could offer a potential for developing a CMOS plasmonic platform and can be designed into various components for future integrated THz circuits (ITCs).

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The simultaneous realization of low propagation loss and subwavelength mode localization remains one of the critical challenges in plasmonics. Aiming to simultaneously realize low propagation loss and subwavelength mode localization in plasmonics, we introduce a class of low-loss and deeply confined guiding schemes utilizing an alternative plasmonic material, i.e., a superconductor (SC). The optical properties of a SC–insulator–SC (SCISC) waveguide are analyzed both at terahertz (THz) and telecommunication (TC) frequencies. The SCISC waveguide features a deep-subwavelength confinement with a mode length as small as λ/6000 (λ/18) for THz (TC) frequency, while the propagation length can be extended up to 400 mm (1 mm).

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A robust plasmonic semiconductor-based Mach-Zehnder interferometer (MZI), which consists of a semiconductor layer with a microslit flanked by two identical microgrooves, is proposed and investigated for the terahertz sensing. The microgrooves reflect the surface plasmon polariton waves toward the microslit, where they interfere with the transmitted terahertz wave. The interference pattern is determined by the permittivities of the sensing material and semiconductor (i.e., temperature dependent), making the structure useful for the refractive index (RI) and temperature detection. A quantitative theoretical model is also developed for performance prediction and validated with a finite element method. The numerical results show that the Mach-Zehnder interferometer sensor possesses an RI sensitivity as high as 140000  nm/RIU (or 0.42  THz/RIU) and a relative intensity sensitivity of 1200%RIU^-1. In addition, a temperature sensitivity of 1470  nm/K (or 4.7×10^-3 THz/K) is determined. Theoretical calculations indicate that the further improvement in sensing performance is still possible through optimization of the structure. The proposed sensing scheme may pave the way for applications in terahertz sensing and integrated terahertz circuits.