Slow surface plasmon pulse excitation in metal-insulator-metal plasmonic waveguide with chirped grating.

Joonsoo Kim,Hwi Kim,Seung-Yeol Lee,Hyeonsoo Park,Byoungho Lee

doi:10.1364/oe.22.018464

Abstract

A scheme for the excitation of slow surface plasmon pulses using photonic interband transition in a metal-insulator-metal (MIM) waveguide is proposed. An investigation the mode transition behavior inside the binary grating confirmed that the proposed concept can be understood in terms of the coupling of symmetric and anti-symmetric plasmonic modes. We observed that, although a binary grating that is optimized for a single frequency can excite slow surface plasmon pulses, it is inadequate for broadband mode conversion. To rectify this, a chirped grating was designed for the demonstration of broadband mode conversion by applying a cascade mode transition with different frequencies.

Highlights

Plasmonics enables the excitation and manipulation of strongly confined electromagnetic fields in the deep subwavelength region
Less attention has been focused on the potential use of non-tapered waveguides, since slow wavepackets will not propagate from one end to the middle of a plasmonic waveguide
The use of a photonic interband transition can be useful for the excitation of slow light pulses inside a waveguide because designing an active device is much easier compared to tapered waveguides

Summary

Introduction

Plasmonics enables the excitation and manipulation of strongly confined electromagnetic fields in the deep subwavelength region. It has been reported that tapered metamaterial waveguides or chirped gratings for spoof plasmons are capable of stopping light of different colors at different positions. The use of a photonic interband transition can be useful for the excitation of slow light pulses inside a waveguide because designing an active device is much easier compared to tapered waveguides. The step would be the design of a spatial permittivity profile that enables efficient conversion to slow light with simple on/off or harmonic temporal modulation. We report on an analysis of the mode transition behavior caused by gratings in MIM waveguides that supports both slow (ng ≈83.1) anti-symmetric plasmonic modes and relatively fast (ng ≈22.6) symmetric plasmonic modes. The Fourier modal method (FMM) which has advantages for modal analysis was used for the simulations throughout this work [18]

Proposed structure and design of MIM waveguide

Design of a binary grating and its pulse response

Nearly perfect transition of the pulse by using chirped grating

Conclusion