Multi-twist retarders: broadband retardation control using self-aligning reactive liquid crystal layers

Ravi K. Komanduri,Kristopher F. Lawler,Michael J. Escuti

doi:10.1364/oe.21.000404

Abstract

We report on a family of complex birefringent elements, called Multi-Twist Retarders (MTRs), which offer remarkably effective control of broadband polarization transformation. MTRs consist of two or more twisted liquid crystal (LC) layers on a single substrate and with a single alignment layer. Importantly, subsequent LC layers are aligned directly by prior layers, allowing simple fabrication, achieving automatic layer registration, and resulting in a monolithic film with a continuously varying optic axis. In this work, we employ a numerical design method and focus on achromatic quarter- and half-wave MTRs. In just two or three layers, these have bandwidths and general behavior that matches or exceeds all traditional approaches using multiple homogenous retarders. We validate the concept by fabricating several quarter-wave retarders using a commercial polymerizeable LC, and show excellent achromaticity across bandwidths of 450-650 nm and 400-800 nm. Due to their simple fabrication and many degrees of freedom, MTRs are especially well suited for patterned achromatic retarders, and can easily achieve large bandwidth and/or low-variation of retardation within visible through infrared wavelengths.

Highlights

Retarders are birefringent elements that can transform polarization by inducing different phase shifts between orthogonal electric-field components of electromagnetic waves
Our analysis reveals that Multi-Twist Retarders (MTRs) are fabricated with standard tools and materials, and achieve excellent optical properties in all cases that correspond well to the simulations above
MTRs represent a new family of phase retarders that can be designed for general polarization manipulation, and are substantially easier to fabricate than prior methods

Summary

Introduction

Retarders are birefringent elements that can transform polarization by inducing different phase shifts between orthogonal electric-field components of electromagnetic waves. They are useful nearly anywhere that polarization [1] is important. Broadband (including achromatic) polarization transformation that can be precisely controlled over a broad range of wavelengths is especially important in applications that involve human perception or multiple simultaneous channels at different wavelengths. The spectral dispersion of the birefringence Δn(λ ) of most optical materials [2] does not in general enable this within one plate; an exception [3] will be discussed later. Several techniques involving multiple birefringent plates have been developed that achieve broadband behavior via the principle of retardation compensation, where a deficiency in the retardation of one plate is at least partially corrected by a subsequent plate

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