Mechanical Manipulation of Diffractive Properties of Optical Holographic Gratings from Liquid Crystalline Elastomers

Abstract

An appealing property of optical diffractive structures from elastomeric materials is a possibility to regulate their optical patterns and consequently also their diffractive features with mechanical straining. We investigated the effect of strain on diffraction characteristics of holographic gratings recorded in a monodomain side-chain liquid crystalline elastomer. The strain was imposed either parallel or perpendicular to the initial alignment direction of the material. At temperatures far below the nematic-paranematic phase transition, straining along the initial alignment affects mainly the diffraction pattern, while the diffraction efficiency remains almost constant. In contrast, at temperatures close to the nematic-paranematic phase transition, the diffraction efficiency is also significantly affected. Straining in the direction perpendicular to the initial alignment strongly and diversely influences both the diffraction pattern and the diffraction efficiency. The difference between the two cases is attributed to shear-stripe domains, which form only during straining perpendicular to the initial alignment and cause optical diffraction that competes with the diffraction from the holographic grating structure.

Nanostructured Composites Based on Liquid-Crystalline Elastomers

“…However, new promising mechanisms based on photo-actuation, magneto-actuation, and “Joule”-heating electrically driven actuation were observed and are described in this review, taking into account very recent works [107,108,109,110,111,112]. Future developments of these polymer composite materials will probably expand to the field of biological applications and biomimetics [65,113,114,115,116], optical tunable gratings [117,118,119], three-dimensional (3D) printing and 3D morphing technologies [20,32,120,121,122], and flexible stretchable electrodes [123,124].…”

Electrically Tuneable Optical Diffraction Gratings Based on a Polymer Scaffold Filled with a Nematic Liquid Crystal

“…Tunability is one of the important properties of diffraction gratings. Various tuning methods have been proposed; diffractive properties can be modulated by an applied electrical voltage [ 25 , 26 , 27 , 28 ], magnetic field [ 29 , 30 , 31 ], pressure, temperature, or by another electromagnetic wave [ 32 , 33 , 34 , 35 , 36 , 37 ]. Liquid crystals (LCs) are very suitable for the construction of tuneable optical diffraction gratings [ 38 , 39 ] since they possess a unique combination of mechanical softness and strong optical anisotropy that provides relatively easy control of LC molecules’ orientation.…”

Multichannel remote polarization control enabled by nanostructured liquid crystalline networks

“…The materials employed in the present work -i.e., polyacrylates -show a nematic-paranematic transition, across which birefringence, stress, and strain change, with a direct impact on the photonic properties of a LCN nanostructure [28,29]. While certain photonic devices based on nanostructured LCN have been already demonstrated [30][31][32][33][34][35][36], our aim is here to illustrate a different application: a remotely controllable multichannel polarization conversion element. It is indeed the important feature of remote, non-invasive tuning that makes our device a significant advancement with respect on previous findings on multichannel photonic components [37].…”