Refracting indices, birefringence and optical dispersion measurements of selected liquid crystals for photonic crystal fibers

Photonic crystal fibers (Microstructured Optical Fibers - MOF) filled with liquid crystals (LCs) offer extended adapting possibility to particular needs in sensing and telecomunication domain. In those optically complex structures many usable effects can be achieved like required shiftting the transmission windows or changing transmission mechanism, affecting the transmitted light polarization and the modal coupling between core and cladding, shaping the mode field etc. LC-infiltrated MOFs enable also outer, continuous control of theirs optical properties. The tunability may be achieved provided that both the refraction indices of LC-substance are properly matched to the index of fiber material in the desired spectral range.
In this work the ordinary and extraordinary indices of the nematic mixtures, prepared for filling PMMA- and PC microstructured fibers, were measured by use of wedge-cell method. This simple goniometric technique is especially useful for LC with large index values, when refractometric methods are approaching their limit. The wedge method requires relatively small amount of LC-substance and gives good results by use of various light sources. The measuring beam hasn’t to be neither coherent nor polarized, while should be well collimated. The results obtained by this method for some new nematic mixtures at several wavelenghts in the visible spectrum were fitted numerically to reconstruct spectral dispersion curves [1].
By the same method the refraction indices of selected ferroelectric LCs were also measured.

[1]. Jun Li, Shin-Tson Wu, “Infrared refractive indices of liquid crystals”, J.Appl.Phys., vol . 97, (2005)