Abstract
Controlling the crystallographic orientation of 3D photonic crystals is important as it determines the behavior of light propagating through the device. Blue phases self-assemble into unique soft 3D photonic crystals with chiral structures for circular-polarization selectivity, but it has remained a challenge to control its 3D orientation. Here, we show that the orientation of blue phases can be precisely controlled to follow a predefined pattern imprinted on a substrate by exploiting field-induced phase transitions. Obtaining the blue phase through the field-induced chiral nematic phase and tetragonal blue phase X results in a highly oriented blue phase I with the crystallographic [001] direction aligned along the surface anchoring. Our approach is applied to fabricating a Bragg-Berry hologram with omnidirectional circular-polarization selectivity, where the hologram is visible only for one circular-polarization under all incident angles. Such devices are difficult to fabricate using conventional optical materials, thereby demonstrating the potential of self-organizing soft matter for photonics.
Highlights
Controlling the crystallographic orientation of 3D photonic crystals is important as it determines the behavior of light propagating through the device
We proposed a facile and robust method to direct the macroscopic self-assembly of blue phase I crystals by exploiting field-induced phase transitions
We found that obtaining blue phase I through two field-induced intermediate phases enables the lattice orientation to be uniquely defined, with (110) crystal plane orientation, and [001] crystal axis orientation along the easy axis
Summary
Controlling the crystallographic orientation of 3D photonic crystals is important as it determines the behavior of light propagating through the device. Our approach is applied to fabricating a Bragg-Berry hologram with omnidirectional circularpolarization selectivity, where the hologram is visible only for one circular-polarization under all incident angles Such devices are difficult to fabricate using conventional optical materials, thereby demonstrating the potential of self-organizing soft matter for photonics. Blue phases are formed by the so-called double twist cylinders (DTCs) of the liquid crystal molecules, and self-organize into chiral cubic structures with body-centered or simple cubic symmetry known as blue phase I and blue phase II, depending on the chiral twisting power and temperature[8] They typically possess a lattice constant of a few hundred nm, giving rise to CP-selective Bragg reflection of incident light with the same CP as the helical structure[9,10]. Our work represents a significant step towards the application of CP-selective optical elements due to its exceptionally wide acceptance angle, and demonstrates the potential of self-organizing soft matter for photonics, enabling functionality that is extremely challenging to realize by top-down nanofabrication of conventional materials
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