Complex vectorial optics through gradient index lens cascades

TL;DR

This paper explores how the inherent birefringence in gradient index lenses can be harnessed in cascaded systems to generate vector vortex beams, improve resolution, and enable a novel polarimeter for cancer diagnostics.

Contribution

It demonstrates the use of GRIN lens birefringence in cascades to create new optical functionalities and a single-shot Mueller matrix polarimeter for biomedical applications.

Findings

Birefringence in GRIN lenses can generate vector vortex beams.

Cascaded GRIN lenses improve axial resolution.

A new polarimeter enables label-free cancer diagnostics.

Abstract

Graded index (GRIN) lenses are commonly used for compact imaging systems. It is not widely appreciated that the ion-exchange process that creates the rotationally symmetric GRIN lens index profile also causes a symmetric birefringence variation. This property is usually considered a nuisance, such that manufacturing processes are optimized to keep it to a minimum. Here, rather than avoiding this birefringence, we understand and harness it by using GRIN lenses in cascade with other optical components to enable extra functionality in commonplace GRIN lens systems. We show how birefringence in the GRIN cascades can generate vector vortex beams and foci, and how it can be used advantageously to improve axial resolution. Through using the birefringence for analysis, we show that the GRIN cascades form the basis of a new single-shot Mueller matrix polarimeter with potential for endoscopic label-free cancer diagnostics. The versatility of these cascades opens up new technological directions.