Achromatic diffraction from polarization gratings with high efficiency

TLDR

The study demonstrates a broadband, thin‑film polarizing beam splitter using an anisotropic diffraction grating of polymerizable liquid crystals. The design employs a stack of two chiral polarization gratings with opposite twist sense and retardation compensation, enabling the diffraction angle and operational wavelength range to be tailored during fabrication. The achromatic polarization grating achieves nearly 100 % diffraction efficiency, an extinction ratio ≥1000:1, and a Δλ/λ₀ ≈ 56 % bandwidth, as confirmed by full optical characterization that matches theoretical predictions.

Abstract

We demonstrate a broadband, thin-film, polarizing beam splitter based on an anisotropic diffraction grating composed of reactive mesogens (polymerizable liquid crystals). This achromatic polarization grating (PG) manifests high diffraction efficiency (approximately 100%) and high extinction ratio (> or = 1000:1) in both theory and experiment. We show an operational bandwidth Deltalambda/lambda0 approximately 56% (roughly spanning visible wavelength range) that represents more than a fourfold increase of bandwidth over conventional PGs (and significantly larger than any other grating). The diffraction angle and operational region (visible, near-infrared, midwave infrared, and ultraviolet wavelengths) may be easily tailored during fabrication. The essence of the achromatic design is a stack of two chiral PGs with an opposite twist sense and employs the principle of retardation compensation. We fully characterize its optical properties and derive the theoretical diffraction behavior.