Self-Organized 3D Photonic Superstructure: Blue Phase Liquid Crystal

Towards complete photonic band gap in a high refractive index nanoparticle-doped blue phase liquid crystal

Three-dimensional (3D) photonic crystals with complete photonic band gap (PBG) are fascinating due to the possibility of controlling light in all directions. Realizing such photonic crystals is nontrivial due to symmetry requirements and associated fabrication challenges. Liquid crystalline cubic blue phases (BPs) are soft 3D photonic crystals with an incomplete PBG due to the low refractive index contrast (<0.1). The present work attempts to drive a cubic BP towards a complete PBG via a simple approach of high refractive index nanoparticle-doping. The photonic band diagrams and reflection spectra of the nanoparticle-doped BP simulated using the finite element method show an increased PBG width, a parameter that quantifies the complete PBG. The reflection spectra obtained from UV-Vis-NIR spectroscopy show an increase (by a factor of >2) in PBG width for the nanoparticle-doped BP, validating the simulations. The findings are explained based on increased refractive index contrast (∼1.4) due to the nanoparticles getting trapped in the cores of disclination lines that make up the BP lattice. The simulations also indicate effective confinement of electric field eigenmodes in the nanoparticle-doped BP leading to high attenuation of the incident light. Further, the iso-frequency contours extracted from the band diagrams exhibit self-collimation and negative refraction of light.

Symmetric Continuously Tunable Photonic Band Gaps in Blue-Phase Liquid Crystals Switched by an Alternating Current Field

Symmetric continuously tunable three-dimensional (3D) liquid photonic crystals have been investigated using self-organized blue-phase liquid crystal films. The photonic band gap in the overall visible spectrum can be tuned continuously, reversibly, and rapidly as the applied electric field changes. After driven by the applied field, four-time enhancement of the reflectivity results in more vivid reflection colors. A lasing emission of tuning working wavelength has been demonstrated by using the dye-doped blue-phase liquid crystal film. With the advantages of fast response speed, no alignment layer, large-scale electrically shift of the photonic band gap, and macro optical isotropy, this self-assembled soft material has many potential applications in high-performance reflective full-color display, 3D tunable lasers, and nonlinear optics.