Tilted Chiral Liquid Crystal Gratings for Efficient Large‐Angle Diffraction. Issue 22 (10th September 2019)

• Record Type: Journal Article
• Authors: Nys, Inge; Stebryte, Migle; Ussembayev, Yera Ye.; Beeckman, Jeroen; Neyts, Kristiaan
• Is Part Of: Advanced optical materials. Volume 7:Issue 22(2019)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2019-09-10
• Subjects: Bragg reflection -- chiral liquid crystals -- periodic photoalignment -- polarization gratings; Optical materials -- Periodicals; Photonics -- Periodicals; 620.11295
• DOI: 10.1002/adom.201901364
• Languages: English
• ISSNs: 2195-1071

Abstract

Abstract: Deflecting light with high efficiency over large angles with thin optical elements is challenging but offers tremendous potential for applications, such as wearable displays and optical communication systems. Compared to the complex production of metasurfaces, the self‐organization of liquid crystal (LC) superstructures provides an elegant and flexible way to produce high‐quality thin optical components. The periodically varying dielectric tensor in short‐pitch chiral LC gives rise to a photonic bandgap, which can be exploited to realize efficient diffractive mirrors in the visible wavelength range. However, large‐angle diffractive devices require a small in‐plane period, leading to complex self‐assembly behavior in the bulk. This work demonstrates that by patterning photoalignment layers at the surfaces with a period comparable to the chiral pitch, the LC self‐assembles into a tilted, defect‐free helical structure. The director configuration is calculated by finite element simulations and it is experimentally demonstrated that a single photoaligned substrate is sufficient to template the tilted chiral structure in the bulk. This structure effectively (88%) diffracts light over large angles (≈46°) and enables novel micrometer‐thin (≈3 µm) optical components that can be produced with an elegant manufacturing process. Due to flexibility of photoalignment, this process could easily be implemented in emerging photonic applications. Abstract : Self‐organization of chiral liquid crystal in cells with photopatterned surface anchoring leads to the realization of highly‐efficient optical components. Micrometer‐thin layers efficiently demonstrate large‐angle diffraction with strong polarization sensitivity. Photopatterning of one or both confining substrates allows to template the tilted chiral bulk structure. The straightforward fabrication process in combination with the versatility of photoalignment offers great perspectives for emerging photonic applications.