Coupling Between Silicon Waveguide and Metal-Dielectric-Metal Plasmonic Waveguide with Lens-Funnel Structure
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Coupling Between Silicon Waveguide and Metal-Dielectric-Metal Plasmonic Waveguide with Lens-Funnel Structure S. Hadi Badri 1
&
M. M. Gilarlue 1
Received: 5 September 2019 / Accepted: 11 November 2019 # Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract Various photonic integrated components have been implemented by ultra-thin silicon-on-insulator (SOI) waveguides; therefore, it is desirable to couple ultra-thin SOI waveguides to plasmonic waveguides. In this paper, we present an ultra-thin SOI waveguide to a metal-dielectric-metal plasmonic waveguide based on a lens-funnel structure consisting of truncated Luneburg lens and metallic parabolic funnel. The lens is implemented by varying the guiding layer thickness. The effect of different parameters of the coupler’s geometry is studied using the finite-difference time-domain method. The 1.13-μm-long coupler improves the average coupling efficiency in the C-band from 66.4 to 82.1%. The numerical simulations indicate that the coupling efficiency is higher than 69% in the entire O, E, S, C, L, and U bands of optical communication. Keywords Strip waveguide . Plasmonic waveguide . Optical coupler . Luneburg lens . All-dielectric metamaterials . Silicon-on-insulator
Introduction Silicon photonic components provide a much broader operational bandwidth compared with the complementary metaloxide semiconductor (CMOS) electronics. Moreover, the SOI waveguides have smaller losses compared with the metallic wires. Therefore, researchers have been trying to replace wires with optical interconnects. However, miniaturizing optical components in the integrated photonic chip is hindered by the diffraction limit. Plasmonic waveguides overcome this obstacle by confining light to a considerably smaller area compared with SOI waveguides at the cost of increased propagation losses [1–3]. Designing an efficient interface between an SOI waveguide and a plasmonic waveguide is crucial to benefit from their advantages. Coupling an SOI waveguide to a metal-dielectric-metal (MDM) plasmonic waveguide has been studied with various methods. A 450 nm × 250 nm (width × thickness) SOI waveguide has been coupled to a 250 nm × 250 nm (slot width × metal thickness) MDM plasmonic waveguide through a 1.7-μm-long taper-funnel structure. The coupling efficiency of this structure is 93.3% at * S. Hadi Badri [email protected] 1
Department of Electrical Engineering, Sarab Branch, Islamic Azad University, Sarab, Iran
1550 nm [4]. A 300 nm × 340 nm SOI waveguide has been coupled to a 200 nm × 200 nm MDM plasmonic waveguide with a 2.5-μm-long taper-funnel coupler. The coupling efficiency of 33% at 1550 nm has been achieved by this method [5]. A 5.2-μm-long coupler has been proposed to couple a 450 nm × 230 nm SOI waveguide to a 200 nm × 180 nm MDM plasmonic waveguide based on a slot-slot coupling scheme. A 50% efficiency at 1640 nm has been measured for this coupler [6]. A 0.4-μm-long coupler has been designed with 93% transmission efficiency at 1550 nm to couple a 300nm-wide silic
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