Ultra-Short Plasmonic Mach-Zehnder Interferometer Based on Air-Slot Coupler

Abstract

Mach-Zehnder interferometers (MZIs) play a crucial role in the development of optical biosensors and densely integrated photonic circuits due to their sensitivity and compatibility with various optical platforms. In this research work, I present systematic design steps and detailed numerical analysis of a very compact plasmonic MZI, which is composed of 3-dB plasmonic splitters of a length of 220 nm positioned between two dielectric waveguides, and integrated with air-slot couplers (ASCs) at both interfaces. The proposed design supports a broad spectral range with a TCE of ~ 87% at 1550 nm. It demonstrates a high tolerance to fabrication variations, which is essential for scalable production and reliable performance in real-world applications. Additionally, by adjusting the positions and widths of the two MDM branches, the MZI can function as a band-stop filter, further expanding its functionality. Moreover, the plasmonic MZI exhibits significant potential for enhanced sensitivity in biosensing applications, offering improved detection of biomolecules due to its strong field confinement and interaction with analytes. Compared to conventional dielectric MZIs, the proposed plasmonic design substantially reduces footprint while maintaining performance. These characteristics make it an ideal candidate for next-generation all-optical plasmonic circuits and biosensing platforms, with potential medical diagnostics and environmental monitoring applications.