Alignment structures and diffraction properties of chiral nematic liquid crystal cells with periodically patterned photoalignment films

Abstract

Liquid crystal (LC) cells with periodic alignment distributions were fabricated using chiral nematic LCs (N*LCs), which were prepared using mixtures of a nematic LC and a chiral dopant, along with photoreactive liquid crystalline polymer (PLCP) films. Periodic structures were formed by polarization holographic recording in the PLCP films. The director distribution in each cell depended on the ratio of chiral dopant present, i.e., the inherent helical pitch of the N*LCs. These periodic alignment structures with line defects in the LC grating cells were well explained on the basis of the elastic continuum theory of the N*LCs and the photoalignment effect of the PLCP films. The diffraction properties of the grating LC cells were also investigated using a polarized visible laser. The observed intensity and polarization states of the diffracted beams were consistent with theoretical ones calculated using the director distribution models. Our results clarify that the diffraction properties of the grating LC cells can be controlled by the helical pitch of the N*LCs.

Visible light, temperature, and electric field-driven rotation of diffraction gratings enabled by an axially chiral molecular switch

“…[15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] The performance of cholesteric DGs is determined by several factors such as the surface alignment of substrates, the helical pitch (P) of CLCs, and so forth. [30][31][32][33][34][35][36][37] Compared with homogeneous alignment or vertical alignment on both substrates of cells, hybrid aligned boundary conditions with one planar aligned surface and another vertical aligned surface provide a spontaneously periodic distortion, resulting in striped domains of CLC gratings oriented unidirectionally. 38 The orientation of these stripes can be continuously rotated in hybrid aligned boundary conditions under different external stimuli, including light, temperature, and electric field.…”

Applied voltage response of a cholesteric liquid crystal cell observed by simultaneous measurement of phase and reflection changes based on optical interferometry

“…The central reflection wavelength and its bandwidth of CP light both depend on the helical structure of the CLC. Since the helical structure of a CLC can be changed by applying voltage, it is expected to be utilized as an active optical device including diffractive elements, 12) laser oscillations, 13,14) and reflective type displays. 15,16) Besides, a few researchers reported that a patterned CLC whose LC directions are spatially distributed on the surface can not only selectively reflect CP light but also convert the wavefront of reflected light corresponding to the LC alignment pattern.…”