Integration of chiral cellulose nanocrystal films in silica optical fibers

Cellulose nanocrystals have attracted great attention as new ‘wonder’ materials for photonic applications owing to their unique property of spontaneous self-assembly to form chiral nematic films. Here, the incorporation of chiral cellulose nanocrystal films on a photonic waveguide is demonstrated for the first time—in the form of integrated silica optical fibers with a helicoid nanocrystal film on their input facet. In order to achieve repeatable cholesteric ordering across the fiber core modal area, a fabrication method was developed where several optical fiber facets form part of a larger flat surface, which acts as the substrate for the planar anchoring of the cellulose nanocrystals. The resultant optical fibers exhibit significant circular dichroism (almost 40%) in transmission and act as all-fiber spectral filters. The proposed fabrication technique provides a simple, low-cost method for developing chiral silica optical fibers that remain compatible with standard telecommunication fiber technology. It is envisioned that the incorporation of cellulose nanocrystals in other optical fiber types will enable the development of a new class of fiber devices.