Improving the electric field sensing capabilities of the long-period fiber grating coated with a liquid crystal layer

The hybrid liquid crystal long-period fiber grating structure presented here uses the 1702 liquid crystal as a thin layer on the bare long-period fiber grating. To achieve the highest long-period fiber grating sensitivity to the liquid crystal layer presence, a UV-induced host grating, with a relatively short period of 226.8 μm, was chosen. This design makes it possible to couple light from the propagating core mode to a cladding mode at a wavelength near the phase-matching turning point. This phenomenon is exploited here for the first time to measure the thermal and electric field responses of the liquid crystal long-period fiber grating structure. All experimental results achieved in this work are supported by theoretical analysis.

Low-loss propagation and continuously tunable birefringence in high-index photonic crystal fibers filled with nematic liquid crystals

Experimental investigations of microstructured fibers filled with liquid crystals (LCs) have so far been performed only by using host fibers made of the silica glass. In this paper, the host photonic crystal fiber (PCF) was made of the PBG08 high-refractive index glass (approximately 1.95) that is much higher than silica glass index (approximately 1.46) and also higher then both ordinary and extraordinary refractive indices of the majority of LCs. As a result, low-loss and index-guiding propagation is observed regardless of the LC molecules orientation. Attenuation of the host PCF was measured to be approximately 0.15 dB/cm and for the PCF infiltrated with 5CB LC was slightly higher (approximately 0.19 dB/cm), resulting in a significant reduction to approximately 0.04 dB/cm of the scattering losses caused by the LC. Moreover, an external transverse electric field applied to the effective photonic liquid crystal fiber (PLCF) allowed for continuous phase birefringence tuning from 0 to 2.10(-4).