Photoalignment of liquid crystal in photonic crsytal fiber by using azo dye.

Abstract

Photonic Crystal Fibers (PCFs) have emerged to be a new class of optical waveguides, which have attracted considerable attention and interest in recent years. PCFs are microstructured waveguides, conventionally made up of silica. They have a large number of air holes located within the cladding region of the fiber. The presence of air holes in the PCF provides a close contact to the fiber core. Thus, by infiltrating new materials into the air holes, a high degree of interaction between light and the material can be achieved and at the same time, maintaining the microstructure of the fiber. However, these micron sized structures impose a problem in the modulation of LC alignment in the air holes.

Thus, in this study, the aim is to investigate the photoalignment of liquid crystal in a photonic crystal fiber by using azo dye. This is attained by infiltrating a nematic LC doped with an azo dye, methyl red (MR) into the PCF air holes to yield PLCF which is later inserted into a Sagnac loop. The Sagnac loop provides a means to observe the LC alignment through a relationship established between LC birefringence and shift of Sagnac interference output minima.

The photoalignment mechanism provided by MR enabled unique interactions between the adsorbed MR molecules and the bulk LC molecules in the PCF. This mechanism can be activated under the irradiation of a green laser light where the MR molecules in the host LC in PCF are photoexcited and undergo a series of transformations. One of the changes that happened is the photoinduced adsorption which resulted in LC realignment, as indicated by the observed shift in the Sagnac interference output minima.