V-shape liquid crystal-based retromodulator air to ground optical communications

TL;DR

This paper introduces a novel free-space optical communication system using a liquid crystal retro-modulator that employs polarization shift keying (PolSK), offering increased bandwidth and robustness against atmospheric visibility changes.

Contribution

It presents the first implementation of PolSK in a liquid crystal-based retro-modulated optical communication link, combining V-shape liquid crystal modulators with retro-reflectors.

Findings

PolSK enhances bandwidth compared to amplitude modulation.

Liquid crystal retro-modulation is effective for free-space optical links.

The system is less sensitive to atmospheric visibility variations.

Abstract

This paper describes the use of a 2D liquid crystal retro-modulator as a free space, wireless, optical link. The retro-modulator is made up of a retro-reflecting cornercube onto which 2 cascaded V-shape smectics liquid crystal modulators are mounted. The communication link differs with respect to more conventional optical links in not using amplitude (nor frequency) modulation, but instead state-of-polarisation (SOP) modulation known as Polarisation Shift Keying (PolSK). PolSK has the advantage over amplitude modulation, that it is less sensitive to changes in the visibility of the atmosphere, and increases inherently the bandwidth of the link. The implementation of PolSK both in liquid crystal based and in retro-modulated communication are novelties.