High-Performance Nano-Sensing and Slow-Light Applications Based on Tunable Multiple Fano Resonances and EIT-Like Effects in Coupled Plasmonic Resonator System

Abstract

A basic plasmonic system, consisting of a stub metal-insulator-metal (MIM) waveguide coupled with a ring resonator, is presented to realize Fano resonance and electromagnetically induced transparency-like (EIT-like) effect, which are numerically calculated by the finite element method (FEM). Meanwhile, the formation mechanism of Fano resonance is analyzed according to numerical simulations. Besides, the coupled mode theory (CMT) and the standing wave theory are used for explaining the Fano and EIT-like resonances phenomenon. Based on this system, an inner ring cavity is connected to the ring resonator by a slot and another ring cavity is later introduced under the stub resonator in order to constitute a new coupled plasmonic resonator system, providing quadruple Fano resonances and double EIT-like responses finally. In addition, the Fano and EIT-like resonances can be independently tuned by adjusting the structural parameters, which makes the design of highly integrated photonic circuits more flexible. The main contribution of this paper is that the proposed structure has a relatively good sensitivity of 1600 nm/RIU and an ultra-high FOM value of 1.2×10 6 as a refractive index nanosensor. Moreover, it can serve as an alloptical switch with a high on/off extinction ratio of about 43 dB. Additionally, its maximum group delay time and group index are about 1.49 ps and 221, indicating that the proposed system has a pretty good slow light effect. Therefore, the proposed structures are believed to have significant applications in high-performance nanosensors, switches, slow light devices and nonlinear areas in highly integrated plasmonic devices. INDEX TERMS Multiple EIT-like effects, multiple Fano resonances, refractive index sensor, surface plasmon polaritons (SPPs), slow light, ultra-high FOM.

A Nanosensor Based on a Metal-Insulator-Metal Bus Waveguide with a Stub Coupled with a Racetrack Ring Resonator

“…According to Equations ( 1)-( 3) and the effective SPPs wavelength, λ SPPs = λ FR /Re(n e f f ), when λ FR = 1729 nm, λ SPPs = 1235 nm, (2πR + 2L)/λ SPPs ≈ 1, which shows that λ SPPs = 1235 nm meets the condition of Fano resonance and conforms to the simulation result when f = 1 [10].…”

“…[15]. k and k 0 are the wave vector in the waveguide and wave vector in free space and k = β 2 − ε Ag k 2 0 , k 0 = 2π/λ FR , β is the propagation constant [5,10,20]. In order to further understand the underlying principle of Fano resonance, the H Z field distributions are studied and plotted in Figure 2b,c.…”

“…where ∆λ is the shift of the resonance wavelength; ∆n is the change in refractive index [10,12,17]. We then analyzed the effects of different similar structures on the transmission spectra and normalized magnetic field H Z .…”

“…[11]. As a kind of similar coherent effect, the EIT-like effect has attracted extensive attention in recent years and has been proved in classical systems such as surface plasmonic devices, photomechanical systems, coupled optical resonators, and metamaterial configurations [10]. Especially in various types of resonant systems, such as microring resonators, microsphere resonators, photonic crystal resonators and isoplason resonators, by designing coherent excitation paths, the interference phenomena similar to the EIT effect can be realized [10,12].…”

“…Electromagnetically induced transparency (EIT) is a kind of quantum interference effect in the atomic field. The interference effect between the ground state to the excited state and the excited state to the metastable state results in a narrow transparent window in the wide absorption spectrum [ 10 ]. EIT in photonics is a coherent optical nonlinearity that makes the medium transparent in a narrow spectral range around the absorption lines.…”