Localised polymer networks in chiral nematic liquid crystals for high speed photonic switching

Abstract

Self-assembled periodic structures based upon chiral liquid crystalline materials have significant potential in the field of photonics ranging from fast-switching optoelectronic devices to lowthreshold lasers. The flexoelectro-optic effect, which is observed in chiral nematic liquid crystals (LCs) when an electric field is applied perpendicular to the helical axis, has significant potential as it exhibits analogue switching in 10-100 ls. However, the major technological barrier that prohibits the commercial realisation of this electro-optic effect is the requirement of a uniform, in-plane alignment of the helix axis between glass substrates. Here, it is shown that periodic polymer structures engineered in the nematic phase of a chiral nematic LC device using direct laser writing can result in the spontaneous formation of the necessary uniform lying helix (ULH) state. Specifically, two-photon polymerization is used in conjunction with a spatial light modulator so as to correct for aberrations introduced by the bounding glass substrates enabling the polymer structures to be fabricated directly into the device. The ULH state appears to be stable in the absence of an externally applied electric field, and the optimum contrast between the bright and dark states is obtained using polymer structures that have periodicities of the order of the device thickness.

Novel liquid crystal photonic devices enabled by two-photon polymerization [Invited]

“…These functional CLCs are promising for low-threshold lasing and multicolor reflections. Another study showed that DLW can generate localized polymer networks in chiral nematic LCs such that uniform lying helix (ULH) state can be spontaneously formed [124]. In a very recent report, DLW was employed to generating images and identification codes in LC device [125].…”

Giant Flexoelectro-optic Effect with Liquid Crystal Dimer CB7CB

“…A well-aligned ULH CLC texture can be obtained by application of pulsed electric field with empirically optimized duration and magnitude to the sample cell91819. Alternatively, a spontaneous formation of the ULH CLC texture have been demonstrated by treatment of the surface of substrates creating periodic micro-grooves1525, periodic anchoring conditions1426, controlling pretilt angle of LC molecules27, periodic polymer channels28 or polymer walls29.…”

Voltage-controlled formation of short pitch chiral liquid crystal structures based on high-resolution surface topography

“…This approach could be further exploited in the future by using different cell thicknesses, different thicknesses of the resist layer and different patterned electrodes and could be very interesting for application in electro-optic devices such as diffraction gratings, lasers and displays. Short pitch ULH-like structures are especially interesting to develop in-plane emitting CLC lasers and displays based on fast flexoelectro-optic switching [18,34,35,36]. Depending on the lateral dimensions that are envisioned, e-beam lithography could also be replaced by conventional UV lithography.…”