Mode-evolution-based polarization rotation and coupling between silicon and hybrid plasmonic waveguides.

Sangsik Kim,Minghao Qi

doi:10.1038/srep18378

Abstract

Hybrid plasmonic (HP) modes allow strong optical field confinement and simultaneously low propagation loss, offering a potentially compact and efficient platform for on-chip photonic applications. However, their implementation is hampered by the low coupling efficiency between dielectric guided modes and HP modes, caused by mode mismatch and polarization difference. In this work, we present a mode-evolution-based polarization rotation and coupling structure that adiabatically rotates the TE mode in a silicon waveguide and couples it to the HP mode in a strip silicon-dielectric-metal waveguide. Simulation shows that high coupling factors of 92%, 78%, 75%, and 73% are achievable using Ag, Au, Al, and Cu as the metal cap, respectively, at a conversion length of about 5 μm. For an extremely broad wavelength range of 1300–1800 nm, the coupling factor is >64% with a Ag metal cap, and the total back-reflection power, including all the mode reflections and backscattering, is below −40 dB, due to the adiabatic mode transition. Our device does not require high-resolution lithography and is tolerant to fabrication variations and imperfections. These attributes together make our device suitable for optical transport systems spanning all telecommunication bands.

Highlights

Hybrid plasmonic (HP) modes allow strong optical field confinement and simultaneously low propagation loss, offering a potentially compact and efficient platform for on-chip photonic applications
Various types of hybrid plasmonic (HP) waveguide configurations based on nano-ridges[21], metal ribbon buried slots[22], and Si-on-nitride gap plasmon[23] have been proposed at mid-infrared (MIR) to take advantage of the reduced propagation loss in plasmonic devices at these longer wavelengths, making HP waveguides attractive for MIR applications such as chemical and biological sensing[24,25,26]
The performance of mode-evolution-based polarization rotation and coupling (PRC) with linear Si taper is evaluated by calculating the coupling factor to the HP mode (CFHP), which is defined as CFHP = PHP02/PTE01, where PTE01 is the input power of TE01 mode at port 1 mode and PHP02 is the output power at port 1; output fields of of HP02 mode HP02 mode is at port 2. 3D decomposed

Summary

Introduction

Hybrid plasmonic (HP) modes allow strong optical field confinement and simultaneously low propagation loss, offering a potentially compact and efficient platform for on-chip photonic applications. Various types of HP waveguide configurations based on nano-ridges[21], metal ribbon buried slots[22], and Si-on-nitride gap plasmon[23] have been proposed at mid-infrared (MIR) to take advantage of the reduced propagation loss in plasmonic devices at these longer wavelengths, making HP waveguides attractive for MIR applications such as chemical and biological sensing[24,25,26] To capitalize on these promising attributes of HP waveguides and integrate this platform into practical systems, requires a highly efficient and robust coupler between HP and Si waveguides to interface with Si photonics. To the best of our knowledge, no such couplers have been reported

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Results

Conclusion