Inverse scattering of 2d photonic structures by layer-stripping

TL;DR

This paper presents a layer-stripping method for reconstructing 2D layered photonic structures using reflectance data, enabling layer-by-layer profiling based on causality and time-domain analysis.

Contribution

It introduces a novel application of layer-stripping to 2D photonic structures, extending seismic and fiber grating techniques to more complex optical systems.

Findings

Successful reconstruction of multi-layer structures in simulations

Effective handling of evanescent modes and bandwidth limitations

Demonstrated layer-by-layer profiling accuracy

Abstract

Design and reconstruction of 2d and 3d photonic structures are usually carried out by forward simulations combined with optimization or intuition. Reconstruction by means of layer-stripping has been applied in seismic processing as well as in design and characterization of 1d photonic structures such as fiber Bragg gratings. Layer-stripping is based on causality, where the earliest scattered light is used to recover the structure layer-by-layer. Our set-up is a 2d layered nonmagnetic structure probed by plane polarized harmonic waves entering normal to the layers. It is assumed that the dielectric permittivity in each layer only varies orthogonal to the polarization. Based on obtained reflectance data covering a suitable frequency interval, time-localized pulse data are synthesized and applied to reconstruct the refractive index profile in the leftmost layer by identifying the local, time-domain Fresnel reflection at each point. Once the first layer is known, its impact on the reflectance data is stripped off, and the procedure repeated for the next layer. Through numerical simulations it will be demonstrated that it is possible to reconstruct structures consisting of several layers. The impact of evanescent modes and limited bandwidth is discussed.