Evaluation of the coupling characteristics of a sandwiched plasmonic waveguide between two dielectric waveguides using air-gap couplers to achieve high-performance optical interconnects

Abstract

. To achieve ultrahigh-density nanoplasmonic integrated circuits, low-loss conventional dielectric waveguides (CDWs) are used to transfer light into and out of the metal–dielectric–metal (MDM) plasmonic waveguides. We show that sandwiching the MDM plasmonic waveguide between two CDWs forms a Fabry–Perot cavity-like structure, which causes oscillations in the transmission coupling efficiency (TCE) into the output CDW as the length of the MDM waveguide is increased. Three types of compact air-gap couplers (AGCs) were used at the interface between those two types of waveguides to enhance the coupling efficiency between them. Our simulation results indicate that tapering CDW before it is connected to AGC not only enhances TCE into the output CDW by 9% over a wide spectrum range but also reduces the need for high-precision fabrication techniques to align AGC at the interface. Moreover, we achieved a TCE into the output CDW of 77% optimized for the optical communications wavelength of 1550 nm when the length of the MDM plasmonic waveguide is 600 nm. In addition, we showed that our proposed design has large fabrication tolerance by investigating the change in its spectrum response as various parameters of the design dimensions differ from that of the targeted optimum dimensions. We found that increasing the dimensions of AGC reduces the width of the spectrum, whereas increasing the width of CDW with its tapered part shifts the spectrum to the right by 100 nm per 40 nm increase in the width. We also found that increasing the refractive index of the MDM plasmonic waveguide with AGC controls the cutoff wavelength, in which TCE is almost zero at wavelengths shorter than the cutoff wavelength, and consequently provides a unique advantage in using our proposed design in sensing applications.

Orthogonal mode couplers for plasmonic chip based on metal–insulator–metal waveguide for temperature sensing application

“…SPP modes have a momentum mismatch with plane waves or conventional dielectric modes, and standard techniques like prisms or Bragg gratings are used to address this issue 20 . However, when dealing with plasmonic MIM waveguide modes, which consist of two closely coupled SPP surface modes, these standard coupling techniques become less practical due to the extremely confined nature of the mode, making it difficult to achieve efficient coupling to the MIM waveguide 21 , 22 . The limited coupling between the silicon waveguide and the MIM waveguide primarily arises from a substantial disparity in the momentum of their fundamental modes.…”

Plasmonic Mach-Zehnder Interferometers Based on Air-Gap Couplers

“…In our study, we begin by examining the impact of sandwiching the MDM plasmonic waveguides between two CDWs by increasing the length of the embedded two MDM plasmonic waveguides and evaluating the TCE into the output CDW. Then, we keep the lengths of the two MDM plasmonic waveguides constant and compare the spectrum responses of different MZI designs to demonstrate that sandwiching the MDM plasmonic waveguide between two CDWs results in a narrowed spectrum response due to the FP cavity-like response [47]. Furthermore, we investigate the fabrication tolerance associated with the proposed MZI that exhibits the highest TCE.…”