Thermodynamically stable non-cubic 3D liquid photonic crystal

Duan-Yi Guo^1*, Cheng-Chang Li¹, Hung-Chang Jau¹, Keng-Hsien Lin¹, Ting-Mao Feng¹, Chun-Ta Wang¹, Tsung-Hsien Lin¹

¹Department of Photonics, National Sun Yat-sen University, Kaohsiung, Taiwan

* Presenter:Duan-Yi Guo, email:alex20150131@gmail.com

Photonic crystal makes advances in manipulating light and finds various applications for optical and photonic systems. Due to the intriguing optical properties, photonic crystal shows great potential in realizing negative refractive index, superprisms, and self-collimation effect, to name a few. Owing to self-assembly, high susceptibility to external stimuli, and sub-micro lattice structure, blue phase liquid crystal (BPLC) is the candidate for obtaining a tunable photonic crystal. However, the thermodynamically stable lattice structures of BPLC are only body-centered cubic (BPI) and simple cubic (BPII). The lattice structure of BPLC exerts a decisive influence on the dispersive relation, so the ability to manipulate the lattice structure is essential. Even though the lattice structure of BPLC can be controlled by an electric field, the non-cubic BPLC tends to be restored to the original state upon the removal of the field. The continuously applied field gives rise to undesired effects such as induced birefringence. Therefore, a method for obtaining thermodynamically stable non-cubic BPLC is on demand. In this work, we successfully enriched the thermodynamically stable lattice structure of BPI by orthorhombic and tetragonal structure by a repetitively applied field (RAF) technique we proposed. We began with the investigation of the dynamics of BPLC responding to an external electric field. It showed a distinct difference between BPI’s and BPII’s dynamics, which is attributed to the configuration of disclinations. Based on this result, we proposed a RAF method to induce stable orthorhombic and tetragonal BPLC which was characterized by optical spectrum, polarized microscopic image and Kossel diagram. The desired lattice structure is obtainable by adjusting the parameters of the RAF method including field strengths and durations. Such non-cubic BPLC can be further stabilized by polymerization. The polymer-stabilized non-cubic BPLC exhibits a giant electro-optic response with a high Kerr coefficient. In sum, the work paves an effective way of fabricating thermodynamically stable non-cubic BPLC. It will be beneficial for the photonic bandgap engineering of BPLC. Additionally, the tailored photonic bandgap of BPLC raises more possibilities for photonic applications.

Keywords: blue phase liquid crystal, photonic crystal, stable non-cubic lattice structure