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Articles you may be interested inFast electro-optic device controlled by dielectric response of planarly aligned cholesteric liquid crystalsThe helical flexoelectro-optic effect produces a submillisecond, temperature-independent in-plane rotation of the optical axis and is potentially interesting for the display industry. The main drawback is that it relies on a texture, the uniform lying helix ͑ULH͒, which is intrinsically unstable. We present a method based on the use of periodic polymeric microchannels to create highly ordered and stable ULH structures. Electro-optic measurements performed on a test device show a large contrast ratio between bright and dark states ͑better then 100:1͒, fast switching ͑200 s͒, and large optical rotation ͑Ͼ30°͒.

The main drawback in the exploitation of the chiral-flexo-electro-optic effect is that it relies on a texture, the Uniform Lying Helix (ULH), which is unstable when the cholesteric is sandwiched between spatially uniform aligning surfaces (UASs). It has been shown that the ULH can be promoted by periodic (horizontal=vertical) anchoring conditions or by the presence of periodic polymeric walls. Here we show that periodic surface relief structures can also promote the formation of a stable ULH texture. The surface relief structure was created by curing an ultraviolet curable material via a two-photon excitation laser-lithography process. The process allows sub-micron resolution and flexibility in creating the topographic relief.

The uniform lying helix (ULH) configuration in cholesteric liquid crystals, where the helical axis of a chiral nematic is aligned uniformly in the plane of two confining substrates is of interest for both electro-optic and photonic applications. However, the formation of the well-aligned ULH structure required is non-trivial. Since the helical axis tends to align at an angle with respect to the surface alignment direction, cells where both substrates have planar alignment layers can cause the formation of a two-domain ULH structure. Here we investigate the orientation and nature of the domains as a function of field application. Further we show that it is possible to obtain mono-domain structures when the alignment directions on each substrate are skewed so as to match the angle that the helix forms with respect to the alignment at the electric field applied. This improves the electro-optic contrast of devices.