Biosensor based on plasmonic Mach-Zehnder interferometer with metallic gratings

Abstract

In this paper, a Mach-Zehnder interferometric sensing structure based on silver nanochains of surface plasmons is optimized. The structure consists of a reference arm, a sensing arm and a nanowire waveguide. Nanowire waveguides are composed of silicon nanowires wrapped with a certain thickness of silver. Introduce two silver nanochains as the reference arm and the sensing arm of the Mach-Zehnder interferometer. And research the transmission characteristics of the designed structure. Improve the accuracy and sensitivity of the designed structure by reducing the transmission loss. Compared with two identical silver nanowires as the reference arm and the sensing arm. After the reference arm and the sensing arm are changed to silver nanochains, the transmission characteristics are significantly improved, and the loss per unit length is obviously reduced. This is because the long-range or coulomb interaction between the unit structures of the silver nano-chains enhances the electromagnetic field in the structure, thereby reducing the transmission loss. We set the lattice constants of the two silver nanochains to different situations. The study found that under the wider width of silicon-coated silver nanowires and certain duty ratios. The unit transmission loss of a structure containing asymmetric silver nanochains is smaller than that of a structure containing symmetric silver nanochains. It can be known that silver nanoparticle chains with small loss can compensate for the transmission loss of silver nanoparticle chains with large loss. Using this feature, we further optimized the design structure and changed one side of the silver nano-chain to nano-wire. Change the lattice constant and duty cycle of the silver nanochain on the other side. We have found that in most cases, this type of structure has better transmission characteristics than a structure containing two silver nanochains and a structure containing two silver nanowires. Our design structure can greatly reduce the transmission loss of the traditional Mach-Zehnder interferometer. Moreover, the fault tolerance rate is high in the preparation process of the structure. It has huge potential application value in practical application.