Transcending shift-invariance in the paraxial regime via end-to-end inverse design of freeform nanophotonics

TL;DR

This paper introduces an end-to-end inverse design approach for nanophotonic imaging systems that break the traditional shift-invariance constraint, enabling high-resolution, noise-robust imaging beyond conventional limits.

Contribution

It presents a novel method combining Maxwell topology optimization with elastic-net reconstruction to design nanophotonic structures that are inherently non-shift-invariant.

Findings

Achieves imaging resolution beyond paraxial shift-invariance limits

Designs nanophotonic structures with non-shift-invariant scattering properties

Demonstrates robust image reconstruction in noisy conditions

Abstract

Traditional optical elements and conventional metasurfaces obey shift-invariance in the paraxial regime. For imaging systems obeying paraxial shift-invariance, a small shift in input angle causes a corresponding shift in the sensor image. Shift-invariance has deep implications for the design and functionality of optical devices, such as the necessity of free space between components (as in compound objectives made of several curved surfaces). We present a method for nanophotonic inverse design of compact imaging systems whose resolution is not constrained by paraxial shift-invariance. Our method is end-to-end, in that it integrates density-based full-Maxwell topology optimization with a fully iterative elastic-net reconstruction algorithm. By the design of nanophotonic structures that scatter light in a non-shift-invariant manner, our optimized nanophotonic imaging system overcomes the limitations of paraxial shift-invariance, achieving accurate, noise-robust image reconstruction beyond shift-invariant resolution.