Electrically tunable plasmon induced transparency in hybrid metal-graphene structures

Abstract

Hybrid metal-graphene structures offer design flexibility to manipulate and control light efficiently. These structures can be used to generate tunable plasmon induced transparency (PIT) in transmission and reflection mode. PIT is plasmonic analogue of electromagnetically induced transparency (EIT). PIT and reflection type PIT (RPIT) devices have been investigated experimentally but they are not tunable, and the numerical investigations of the tunable designs were limited to simulations. A hybrid metal-graphene design is used to overcome these challenges in this thesis. Tunable PIT and RPIT devices can be used for tunable enhanced biosensing and switchable systems. PIT-effect has been numerically investigated and experimentally realized in two devices with different dimensions. Numerical simulations were performed using Finite Difference Time-Domain (FDTD) method. The design is based on two parallel gold (Au) strips on top of the graphene layer. PIT-effect has been achieved by weak hybridization of two bright modes of these Au strips. The PIT-effect is tuned by changing the Fermi energy (Ef) of graphene. Top gating method is used to achieve high tunability in the experiments. Total shift of 263 nm is obtained in the PIT window by applying the gate voltage up to 3 V. The spectral contrast ratio of the devices is up to 82%. In addition, tunable RPIT effect is achieved using the same metal-graphene structure. I have numerically investigated the four layers design and experimentally realized tunable RPIT. The response of this device is also tuned using top gating method. The tunability of 220.8 nm is observed in RPIT peak for 3 V.