Abstract
We present an experimental and theoretical investigation of the optical diffractive properties of electrically tuneable optical transmission gratings assembled as stacks of periodic slices from a conventional nematic liquid crystal (E7) and a standard photoresist polymer (SU-8). The external electric field causes a twist-type reorientation of the LC molecules toward a perpendicular direction with respect to initial orientation. The associated field-induced modification of the director field is determined numerically and analytically by minimization of the Landau–de Gennes free energy. The optical diffraction properties of the associated periodically modulated structure are calculated numerically on the basis of rigorous coupled-wave analysis (RCWA). A comparison of experimental and theoretical results suggests that polymer slices provoke planar surface anchoring of the LC molecules with the inhomogeneous surface anchoring energy varying in the range 5–20 μJ/m2. The investigated structures provide a versatile approach to fabricating LC-polymer-based electrically tuneable diffractive optical elements (DOEs).
Highlights
Diffractive optics is an important field of modern optics that deals with optical elements whose function is based on optical diffraction phenomena [1]
This work presents an experimental and theoretical investigation of the optical diffraction properties of electrically tuneable diffraction gratings fabricated from a commercial nematic Liquid crystals (LCs) mixture (E7) and a standard photoresist polymeric material (SU-8)
The investigated periodically modulated structure was based on periodic slices of the nematic liquid crystal E7 and the photoresist polymer SU-8
Summary
Diffractive optics is an important field of modern optics that deals with optical elements whose function is based on optical diffraction phenomena [1]. This work presents an experimental and theoretical investigation of the optical diffraction properties of electrically tuneable diffraction gratings fabricated from a commercial nematic LC mixture (E7) and a standard photoresist polymeric material (SU-8). The innovation of this approach is that the polymeric material is present in the volume of the grating structure and on its surfaces, as is the case in photoalignment-based LC gratings. The orientational structure of the LC medium, located inside the periodic polymeric scaffold as a function of an applied external electric field, is calculated by minimization of the Landau–de Gennes free energy [53,54,55]. DOEs and simulations of their operation controlled by an external electric field
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