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

Self-assembled periodic structures based upon chiralliquid crystalline materials have significant potential in the field of photonics ranging from fast-switching optoelectronic devices to low-threshold lasers. The flexoelectro-optic effect, which is observed in chiralnematic 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 μs. However, the major technological barrier that prohibits the commercial realisation of this electro-opticeffect 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

Stabilizing the uniform lying helix alignment in chiral nematic liquid crystals using direct laser writing

We investigate a novel approach for controlling the alignment of a fast-switching chiral nematic liquid crystal state using a high resolution two-photon absorption laser scanning lithography technique with aberration correction that permits the engineering of photonic structures in-situ. Walls of polymer network are engineered parallel and perpendicular to the helical axis of a uniform lying helix in chiral nematic liquid crystals in order to stabilize the alignment in the absence of an electric field and enhance the flexo-electro-optic response

Generation of 3-dimensional polymer structures in liquid crystalline devices using direct laser writing

Direct laser writing is a powerful nonlinear fabrication technique that provides high intensities in the focal plane of a sample to engineer multidimensional structures with submicron feature sizes. Dielectrically and optically anisotropic soft matter is of particular interest when considering a host medium in which exotic topological characteristics may be generated. In this manuscript, we adopt a novel approach for direct laser writing of polymeric structures, whereby the photo-sensitive resin is liquid crystalline (LC) and aligned within electrically addressable LC devices. We show that the laser written polymer structures retain the optical properties of the liquid crystal resin at the point of laser exposure. Thus, birefringent polymer structures can be written, with the orientation of the optic axis tuned during fabrication through switching the liquid crystal with an applied electric field. This gives the potential to create complex spatial variations of the polymer refractive index on a micron scale. Furthermore, we present a range of structures for controlling the liquid crystal alignment in devices, including two-dimensional arrays of polymer pillars, a polymer checkerboard that creates a controllable disclination network, and 3-dimensional helical polymer ribbons and knots. This work introduces a new degree of freedom for the direct laser writing of advanced photonic materials as well as offering significant advances for the control of soft matter.The authors gratefully thank the Engineering and Physical Sciences Research Council (UK), Merck Chemicals Ltd, the Leverhulme Trust and The Royal Society for financial support

Read on demand images in laser‐eritten polymerizable liquid crystal devices

Two‐photon laser writing is a powerful technique for creating intricate, high resolution features in polymerizable materials. Here, using a single‐step process to microfabricate polymer inclusions, the ability to generate read‐on‐demand images and identification codes in a liquid crystal (LC) device is demonstrated. These micrometer‐sized polymer features are encoded directly into LC devices using direct laser writing, which locks‐in the local molecular orientation at the moment of fabrication. By reading the devices with the same voltage amplitude that is used to write the polymer structures, features can be made to disappear as the director profile becomes homogeneous with the surrounding regions, effectively cloaking the structure for both polarized and unpolarized light. It is shown how this process can be used to create micrometer‐scale reconfigurable emoticons and quick‐response codes within a fully assembled LC device, with potential use in authenticity and identification applications

Read on demand images in laser‐eritten polymerizable liquid crystal devices

Two‐photon laser writing is a powerful technique for creating intricate, high resolution features in polymerizable materials. Here, using a single‐step process to microfabricate polymer inclusions, the ability to generate read‐on‐demand images and identification codes in a liquid crystal (LC) device is demonstrated. These micrometer‐sized polymer features are encoded directly into LC devices using direct laser writing, which locks‐in the local molecular orientation at the moment of fabrication. By reading the devices with the same voltage amplitude that is used to write the polymer structures, features can be made to disappear as the director profile becomes homogeneous with the surrounding regions, effectively cloaking the structure for both polarized and unpolarized light. It is shown how this process can be used to create micrometer‐scale reconfigurable emoticons and quick‐response codes within a fully assembled LC device, with potential use in authenticity and identification applications