Liquid crystals open new route to planar optical elements

Researchers at Osaka university developed a generation to control the mild wavefront meditated from a cholesteric liquid crystal -- a liquid crystal section with a helical structure. although acknowledged for their capacity to Bragg-replicate mild, cholesteric liquid crystals may want to simplest be used as flat mirrors, reflecting mild on the same perspective as the incident angle. the brand new technology allows planar optical additives to be made with functionality with the aid of design, contributing to the miniaturization of catoptrics devices.

The cholesteric liquid crystal is a liquid crystal section in which the constituent rod-like molecules spontaneously form a helical shape. attributable to its structure, cholesteric liquid crystals exhibit Bragg-reflection for circularly polarized light with the same polarization handedness because the helix, over a wavelength range decided by the refractive index and the helical pitch. Their characteristic optical homes, in addition to the fact that shape is shaped by using self-organization, have made cholesteric liquid crystals appealing for use as round polarizers, mild reflectors, and electronic papers. however, their capability to characteristic handiest as a flat dielectric mirror in which light have to follow the law of reflection posed a limit on the overall performance they might acquire, and therefore utilization of gadgets based on these substances.

Hiroyuki Yoshida, Assistant Professor, Junji Kobashi, a graduate student, and Masanori Ozaki, Professor at Graduate school of Engineering, Osaka university discovered that the optical section contemplated from a cholesteric liquid crystal various relying at the segment of the helical structure. The distribution of optical segment (additionally referred to as the wavefront) determines how the mild propagates; as an example, mild propagating alongside a directly line has a flat profile, while mild that converges has a curved (parabolic) profile. on the other hand, the helix phase defines the relative orientation of the helical shape at a particular function in area, and can without problems be controlled by defining the orientation of the liquid crystal molecules on a substrate. therefore, with the aid of patterning the orientational smooth axis in a preferred, slab-like cholesteric liquid crystal device, the meditated wavefront may be designed arbitrarily.

The photo illustrates a planar lens device primarily based in this concept; the parabolic distribution of the helix segment converts an incident planar wavefront to a parabolic profile that converges at a single factor. The device suggests high round polarization selectivity even if the helix segment is patterned; the generation hence gives a platform to develop particular optical devices that can be tuned from being completely reflective to transmissive, relying on the incident polarization.