Helical Nanostructures of Ferroelectric Liquid Crystals as Fast Phase Retarders for Spectral Information Extraction Devices: A Comparison with the Nematic Liquid Crystal Phase Retarders

Abstract

Extraction of spectral information using liquid crystal (LC) retarders has recently become a topic of great interest because of its importance for creating hyper- and multispectral images in a compact and inexpensive way. However, this method of hyperspectral imaging requires thick LC-layer retarders (50 µm–100 µm and above) to obtain spectral modulation signals for reliable signal reconstruction. This makes the device extremely slow in the case of nematic LCs (NLCs), since the response time of NLCs increases proportionally to the square of the LC-layer thickness, which excludes fast dynamic processes monitoring. In this paper, we explore two approaches for solving the speed problem: the first is based on the use of faster nanospiral ferroelectric liquid crystals as an alternative to NLCs, and the second is based on using a passive multiband filter and focuses on multispectral extraction rather than hyperspectral. A detailed comparative study of nematic and ferroelectric devices is presented. The study is carried out using a 9-spectral bands passive spectral filter, covering the visible and near-infrared ranges. We propose the concept of multispectral rather than hyperspectral extraction, where a small number of wavelengths are sufficient for specific applications.

Faster narrowband multi-spectral liquid crystal-based imaging modules tailored to the specific application

“…Spectral imaging systems allow the capture of a scene with several objects and perform spectral analysis at every point in space for all objects simultaneously, therefore improving the capabilities and performances of such systems. For many applications, the essential spectral information resides in a few discrete wavelengths that are known in advance, hence, an application-oriented multispectral system can collect the information more efficiently and provide better performance than a hyperspectral system [3].…”

Faster Multispectral Imager Based on Thin Liquid Crystal Modulator and 3D Neural Network Lattice

“…Other cases are in scenarios where the examined objects can be characterized based on only few or several spectral bands in a known accurate spectral location and a known spectral width. [ 14 ] For these reasons, a multispectral system would be preferable over a system with a higher spectral separation, which can lead to higher acquisition rates, signal‐to‐noise ratio (SNR) improvement, higher spatial resolution, processing, and storage size reduction. In what follows we give a short summary of the advantages and limitations of compressive sensing versus deep learning approaches, while for more detailed discussion the reader is referred to the Supporting Information.…”

High Light Efficiency Spectral Polarization Imaging Method Based on Mach–Zehnder Structured Liquid Crystal Tunable Filters and Variable Retarders

“…August et al [29] proposed an approach using a single LCVR to modulate and achieve the reconstruction of hyperspectral images. Alternatively, AbuLeil et al [30] explored the parallel spectroscopic extraction using spectral modulation and computational algorithms formed by LCVRs or multi-band pass filters. However, the drawback of this means is that it inadequately compresses the hyperspectral image data in the spatial domain.…”