Propagation properties of photonic liquid crystal fibers infiltrated with highly nonlinear materials

It is almost two decades since photonic crystal fibers (PCFs) with their unique features are subjected to intense scientific investigations, finding thus a wide range of potential applications in many areas of science and technology. While propagation properties of PCFs can be dynamically changed by introducing gaseous, liquids or solid materials into their air-channels, this simple idea has been proven to be very useful for broadening the applicability of PCFs. Specifically, the concept of using liquid crystals (LCs) for infiltration, resulting in new type of fibers referred to as photonic liquid crystal fibers (PLCFs), is of particular attention. Liquid crystals used as inclusions allows the optical parameters of PLCFs to be dynamically adjusted by external fields and factors (e.g. by electric and magnetic fields, temperature, strain and pressure) and/or by light beams themselves (when nonlinear effects are considered in LCs).
In this work, results of experimental tests on the light propagation in PLCFs are presented. While refractive index of typical LC is higher than that of silica glass, analyzed photonic structure can be considered as a matrix of mutually parallel waveguide channels. This connotes discrete light propagation to be observed in PLCFs, with the output beam profile strongly dependent on geometrical and optical properties of both the beam and the fiber. In particular, we focus on tunability of the beam guidance obtained due to the variation in either external temperature or optical power (with assumption of thermal nonlinearity taking place in liquid crystals). It has been demonstrated that discrete light propagation in PLCFs can be tuned by varying optical power of the signal optical beam. Experimental results, acquired with use of the signal beam from CW Nd:YAG (1064nm)/DPSS (532nm) laser confirm a power-dependence of the beam profile at the output facet of PLCF. Specifically, highly tunable (discrete) diffraction and thermal self-(de)focusing has been tested in experimental conditions. In addition, a weak collinear probe at the different wavelength has been also applied to monitor how the waveguide channel(s) is (are) decoupled from the rest of the matrix.