Development of Cholesteric Liquid-Crystal Spectral Filters for Visible WDM Channels Over Polymer Optical Fibres

This paper describes the development of notch filters and dichroic beam-splitters, the latter to be a visible 2-channel WDM Multiplexer/Demultiplexer (MUX/DEMUX). Both discrete devices are intended to be used on very short-haul links based on Poly-Methyl-Methacrylate (PMMA) Polymer Optical Fibres (POFs). The filters were built from commercially available multilayer dielectric stack and also from engineered Cholesteric Liquid Crystals (CLCs). The latter was manufactured by using nematic LC doped with appropriate chiral dopant. In order to have the reflection of above 80% for the desired wavelength and also for non-polarised light we used approximately 20 layers of CLC with both helicities in a planar Grandjean texture. The CLC with left handed helix will reflect left circularly polarised light, while the right handed helix will reflect the right handed circularly polarised light.