Plasmonic Tamm states: dual enhancement of light inside the plasmonic waveguide

Abstract

A type of Tamm states inside metal-insulator-metal (MIM) waveguides is proposed. An impedance based transfer matrix method is adopted to study and optimize it. With the participation of the plasmonic Tamm states, fields could be enhanced twice: the first is due to the coupling between a normal waveguide and a nanoscaled plasmonic waveguide and the second is due to the strong localization and field enhancement of Tamm states. As shown in our 2D coupling configuration, |E| 2 is enhanced up to 1050 times when 1550 nm light is coupled from an 300 nm Si slab waveguide into an 40 nm MIM waveguide. Optical Tamm states (OTSs, also known as Tamm plasmons), was recently discovered at the interface between a metal film and an 1D photonic crystal (PC) [21,22]. Unlike the only TM-polarized SPPs, OTSs can be excited directly by normal incidence for both TM and TE-polarized waves. The light frequency lies in the band gap of the PC. Fields are confined and amplified at the metal/PC interface due to the interference of light reflected from both sides. Owing to the strong field enhancement, applications such as lasers [23,24], all-optical switches [25], solar cells [26], Faraday rotation [27,28] and electromagnetically induced transparency (EIT) [29] have been proposed.In this letter, we introduce and demonstrate a type of Tamm states in plasmonic metal-insulator-metal (MIM) waveguides. In analogy with OTSs in an optical system, such states exist in a plasmonic system, as which we call plasmonic Tamm states (PTSs). We form Bragg reflectors (BR) by periodically change the dielectric materials in MIM [30]. Only if the phase matching condition r left r right = 1 is fulfilled, PTSs can be generated in accompany with fields enhancement at the interface between the MIM BR and the MIM end [21]. Hence, fields can be enlarged twice during the focusing process: the first enhancement is due to the coupling between a normal dielectric waveguide and a nanoscaled MIM waveguide and the second enhancement is due to the strong localization and amplification of PTSs. Fig. 1. Sketch of the plasmonic Tamm states generation configuration. In order to fulfill the phase matching condition, ε 2 should be larger than ε 1 .The scheme of the PTSs generation configuration is illustrated in Fig. 1. SPPs are excited at the left side. The operation wavelength is 1550 nm. The dielectric core has a width of w = 40 nm. In this regime, the odd TM mode (E x is odd, E y and H z are even) is the only mode of this MIM structure with a dispersion relation [4]where ε m and ε d are the dielectric constants of the metal and the dielectric, respectively. k m and k d denote the re-1 arXiv:1401.5230v1 [physics.optics]

Nanofocusing of the free-space optical energy with plasmonic Tamm states

“…Then, the time-consuming FDTD calculation is performed to determine the best values of d 1 and d 2 around the values found by the TMM. It has been shown that the TMM results match well with full-wave simulations13. In our case, as shown in Fig.…”

“…It should be noted that small numbers of periods are not able to confine enough energy at the BR terminal, and long MIM waveguides will introduce more Ohmic loss13. In Fig.…”

“…Plasmonic Tamm states (PTSs)13, a newly discovered type of Tamm states, have been proposed as an effective solution to produce strong field enhancement. Unlike optical Tamm states (OTSs, also known as Tamm plasmons)14 that can be excited directly by both TE- and TM-polarized waves in an optical system, PTSs exist in a plasmonic system and can only be excited by TM-polarized waves.…”

On the tunability of quality-factor for optical Tamm plasmon modes

“…It is also important to note that the full-width at half-minima (FWHM) or linewidth of OTP resonance decreases as N and d m increase. This is primarily a consequence of overall increase in reflectivity of the Ag-DBR geometry resulting in improved finesse for Ag-DBR cavity [32,33]. Therefore, the reduction in linewidth with increase in DBR pairs indicates that Ag-DBR architecture, with more number of bilayers (N) or thicker metal layer, will provide a better platform for increasing the Q-factor of OTP mode.…”