Theoretical Investigation of an Air-Slot Mode-Size Matcher between Dielectric and MDM Plasmonic Waveguides

Rami A Wahsheh,Rujiang Li

doi:10.1155/2021/1025374

Abstract

Hybrid integration of dielectric and plasmonic waveguides is necessary to reduce the propagation losses due to the metallic interactions and support of nanofabrication of plasmonic devices that deal with large data transfer. In this paper, we propose a direct yet efficient, very short air-slot coupler (ASC) of a length of 36 nm to increase the coupling efficiency between a silicon waveguide and a silver-air-silver plasmonic waveguide. Our numerical simulation results show that having the ASC at the interface makes the fabrication process much easier and ensures that light couples from a dielectric waveguide into and out of a plasmonic waveguide. The proposed coupler works over a broad frequency range achieving a coupling efficiency of 86% from a dielectric waveguide into a metal-dielectric-metal (MDM) plasmonic waveguide and 68% from a dielectric waveguide to an MDM plasmonic waveguide and back into another dielectric waveguide. In addition, we show that even if there are no high-precision fabrication techniques, light couples from a conventional dielectric waveguide (CDW) into an MDM plasmonic waveguide as long as there is an overlap between the CDW and ASC, which reduces the fabrication process tremendously. Our proposed coupler has an impact on the miniaturization of ultracompact nanoplasmonic devices.

Highlights

Efficient coupling of light into a metal-dielectric-metal (MDM) waveguide from a conventional dielectric waveguide (CDW) is the future of the on-chip applications of the plasmonic devices such as splitters [1, 2], Mach–Zehnder interferometers [3, 4], reflectors [5], wavelength demultiplexers [6], circulators [7], filters [8], and all-optical switching [9]
One solution in the literature that has attracted a lot of attention is proposed using a very compact air-gap coupler (AGC) at the interface between a MDM plasmonic waveguide and CDW [21]. e proposed AGC provided a large fabrication tolerance in addition to high transmission coupling efficiency (TCE) into the output dielectric waveguide
Another solution that attracted a lot of attention, because of its simple and compact design, is the air-slot coupler (ASC) that we proposed in [22]. e proposed ASC was fabricated between a 460 nm-wide silicon waveguide and 80 nm-wide gold-air-gold plasmonic waveguide. e TCE was about 40% when the length of the MDM waveguide was 500 nm. e proposed ASC couples light from the CDW into the ASC waveguide before it is coupled into the MDM plasmonic waveguide. e air-slot waveguide that is located inside the CDW at the interface with the MDM plasmonic waveguide is the ASC

Summary

Introduction

Efficient coupling of light into a metal-dielectric-metal (MDM) waveguide from a conventional dielectric waveguide (CDW) is the future of the on-chip applications of the plasmonic devices such as splitters [1, 2], Mach–Zehnder interferometers [3, 4], reflectors [5], wavelength demultiplexers [6], circulators [7], filters [8], and all-optical switching [9]. E proposed AGC provided a large fabrication tolerance in addition to high transmission coupling efficiency (TCE) into the output dielectric waveguide Another solution that attracted a lot of attention, because of its simple and compact design, is the air-slot coupler (ASC) that we proposed in [22]. Our proposed ASC #4 with the WSi width expansion can be used in different sensing applications to show that the refractive index of the slot waveguide, nSlot As nSlot increases, the TCE decreases, and the shape of the spectrum changes as a result of the poor coupling from the CDW into the slot waveguide in addition to the oscillations in the slot waveguide that behaved like an FP cavity-like structure. As nSlot increases, the TCE decreases, and the shape of the spectrum changes as a result of the poor coupling from the CDW into the slot waveguide in addition to the oscillations in the slot waveguide that behaved like an FP cavity-like structure. e TCE value is zero from about 950 nm to about 1150 nm for all types of nSlot

Analysis of the Sensitivity of the Design to Different Fabrication Challenges

Findings

Conclusions