Chromatic control in coextruded layered polymer microlenses

TL;DR

This paper presents a novel method to create layered polymer microlenses with tunable chromatic dispersion by combining multilayer coextrusion, photolithography, and theoretical modeling, enabling control over focal length variation.

Contribution

It introduces a new approach to fabricate layered microlenses with adjustable chromatic properties using multilayer coextrusion and photolithography, supported by theoretical analysis.

Findings

Focal length varies by nearly 25% across a 50 nm reflection band.

Layered structure enhances chromatic dispersion control.

Microlenses of 56 microns diameter achieve a 300-micron focal length.

Abstract

We describe the formation, characterization and theoretical understanding of microlenses comprised of alternating polystyrene and polymethylmethacrylate layers produced by multilayer coextrusion. These lenses are fabricated by photolithography, using a grayscale mask followed by plasma etching, so that the refractive index alternation of the bilayer stack appears across the radius of the microlens. The alternating quarter-wave thick layers form a one-dimensional photonic crystal whose dispersion augments the material dispersion, allowing one to sculpt the chromatic dispersion of the lens by adjusting the layered structure. Using Huygen's principle, we model our experimental measurements of the focal length of these lenses across the reflection band of the multilayer polymer film from which the microlens is fashioned. For a 56 micron diameter multilayered lens of focal length 300 microns, we measured a nearly 25 percent variation in the focal length across a shallow, 50 nm-wide reflection band.