Controlling evanescent waves using silicon photonic all-dielectric metamaterials for dense integration

Saman Jahani,Sangsik Kim,Vien Van,Abdullah Al Noman,Ward D Newman,Raymond G Decorby,Prashant Shekhar,Minghao Qi,Kyunghun Han,Justin C Wirth,Lukas Chrostowski,Zubin Jacob,Farid Kalhor,Jonathan Atkinson

doi:10.1038/s41467-018-04276-8

Abstract

Ultra-compact, densely integrated optical components manufactured on a CMOS-foundry platform are highly desirable for optical information processing and electronic-photonic co-integration. However, the large spatial extent of evanescent waves arising from nanoscale confinement, ubiquitous in silicon photonic devices, causes significant cross-talk and scattering loss. Here, we demonstrate that anisotropic all-dielectric metamaterials open a new degree of freedom in total internal reflection to shorten the decay length of evanescent waves. We experimentally show the reduction of cross-talk by greater than 30 times and the bending loss by greater than 3 times in densely integrated, ultra-compact photonic circuit blocks. Our prototype all-dielectric metamaterial-waveguide achieves a low propagation loss of approximately 3.7±1.0 dB/cm, comparable to those of silicon strip waveguides. Our approach marks a departure from interference-based confinement as in photonic crystals or slot waveguides, which utilize nanoscale field enhancement. Its ability to suppress evanescent waves without substantially increasing the propagation loss shall pave the way for all-dielectric metamaterial-based dense integration.

Highlights

Ultra-compact, densely integrated optical components manufactured on a CMOS-foundry platform are highly desirable for optical information processing and electronic-photonic cointegration
The skin-depth in the cladding of e-skid waveguide is shorter compared to the other structures due to the strong effective anisotropy of the multilayer cladding. This counterintuitive approach can have a cladding with a higher average index than the core and marks a departure from interference-based confinement as in photonic crystal waveguides or slot waveguides which utilize nanoscale field enhancement
We have shown that highindex contrast grating structures in the deep sub-wavelength limit can act as an all-dielectric metamaterial cladding for simultaneously achieving total internal reflection (TIR) and controlling the skin-depth of evanescent waves

Summary

Introduction

Ultra-compact, densely integrated optical components manufactured on a CMOS-foundry platform are highly desirable for optical information processing and electronic-photonic cointegration. Photonic crystal waveguides can confine light inside a line defect due to Bragg reflection[40] (Fig. 1b) These waveguides perform efficiently at very sharp bends[41], the integration density is limited as the periodicity of Bragg reflectors is on the order of the wavelength and it cannot be perturbed by another waveguide nearby[42]. To satisfy the continuity of the normal component of the displacement current at the high-contrast interface, the electric field peaks inside the gap, leading to light confinement but at the cost of skin-depth expansion in the cladding This causes cross-talk between adjacent waveguides and radiation loss at sharp bends in dense photonic-integrated circuits. A new low-loss and scalable platform is needed for CMOS-foundry compatible dense photonic integration with low cross-talk and reduced bending loss

Objectives

Methods

Results

Conclusion