Direction-dependent optical modes in nanoscale Silicon waveguides

Jacob T Robinson,Michal Lipson

doi:10.1364/oe.19.018380

Abstract

We show that in high-index-contrast nanoscale waveguides counter propagating waves can posses distinct spatial near-field profiles. Using transmission-based near-field scanning optical microscopy (TraNSOM), we identify and map the unique near-field intensity distributions of these counter-propagating modes in a single-mode silicon waveguide. Based on this phenomenon, we design and simulate an integrated device 45 µm in length that selectively attenuates reflected light with an insertion loss of -3.6 dB and an extinction of greater than -20 dB.

Highlights

Using near-field microscopy, we show that in nanophotonic waveguides forwardpropagating and reflected waves are spatially distinct
We show that unlike fiber-optic waveguides, the high-index-contrast and nanoscale dimensions of semiconductor waveguides create counter propagating waves with distinct spatial near-field profiles
While scanning the waveguide with an Atomic Force Microscope (AFM) probe we constantly monitor the power transmitted through the device

Summary

Introduction

Using near-field microscopy, we show that in nanophotonic waveguides forwardpropagating and reflected waves are spatially distinct. If the mode profiles of the forward-propagating and reflected waves are identical (as is expected for low-index waveguides like fiber optics) we should observe that scattering by the probe only decreases the transmitted power. This is because at every point across the waveguide, the probe would interact simultaneously with both forward-propagating and reflected light. This verifies that the measured increase in transmission is the result of interaction with the backward-propagating reflected light in the guided mode.

Objectives

Methods