Geometric phase device writing on a nematic LC cell by using polarization holography

In this paper, we propose to fabricate the Geometric Phase (GP) optical device in a Nematic Liquid Crystal cell (NLC cell) by using photo-alignment technique with poly [1- [4-(3-carboxy-4-hydroxyphenylazo)benzenesulfonamido]-1,2- ethanediyl, sodium salt] azo-polymer (PAZO) as alignment layer. During fabrication, the necessary surface alignment pattern of GP modulations for the device is firstly created and written on the PAZO films of an empty cell by using polarization holographic method. With filling E7 LC molecule, GP grating and lens are formed. The design principle, fabrication and characterization of both GP diffractive grating and lens are presented. The results show that the device can appear as a polarization-selective transmission hologram with single diffractive order, although the thickness of cell is 5 μm. In addition, the polarization state and wavefront of diffracted wave can be converted simultaneously. Thus, the device can be named as the diffractive waveplate, which provides many unique photonic applications, becoming effective way for minimizing and integrating optical devices for a photonic modular.