Periodic liquid crystalline waveguiding microstructures

Different methods allowing for creating optical waveguides with liquid-crystal (LC) cores, in which molecules form periodic patterns with precisely controlled periods, are reported. The first one is based on reversible photoalignment with high-resolution selective illumination and allows to control the period of LC molecules inside silica microcapillaries. The second method employs microstructures formed in PDMS, allowing to obtain both: LC-core waveguides and a set of specially designed periodic microelectrodes used for the periodic reorientation of molecules. Using both methods, we successfully controlled the period of the patterned alignment in the range from about 500 mu m and scaled it down to as small as 20 mu m. We performed experimental studies on waveguiding phenomenon in such structures, in view to obtain transmission spectra typical to optical fiber gratings. Since the results achieved in experimental conditions differed from those expected, the additional numerical simulations were performed to explain the observed effects. Finally, we obtained the waveguiding in a blue phase LC, characterized by naturally created three-dimensional periodicity with periods smaller than one micrometer. In such a structure, we were able to observe first-order bandgap, and moreover, we were able to tune it thermally in nearly the whole visible spectral range.

Automated summary

Different methods for creating optical waveguides with liquid-crystal cores, including reversible photoalignment and microstructure methods, were investigated. The period of the patterned alignment was controlled using selective illumination and microelectrodes. Experimental studies and numerical simulations were performed to understand the waveguiding phenomenon. Waveguiding in blue phase liquid crystal with tunable first-order bandgap was achieved.