Polarization grating using photoalignable liquid crystalline polymer and control of its birefringence

Photoalignable liquid crystalline polymers (PLCPs) exhibit molecularly oriented structure for their own by means of axisselective photoreaction followed by self-organization, which is so-called bulk photoalignment. We investigated various types of PLCPs and applied them to birefringent optical films. This paper presents a photoinduced bulk photoalignment of a PLCP containing chemically reactive mesogenic side groups, which shows significant molecular orientation and photoinduced birefringence greater than 0.4. Using the ~700 nm-thick PLCP films, polarization grating (PGs) with a periodicity of 794 nm were fabricated. The PGs exhibit high diffraction efficiency up to 91%, and the angular acceptance of full width of half maximum (FWHM) of the diffraction efficiency is approximately 45°. Furthermore, slantwise and double slantwise PGs are fabricated by means of slantwise holographic exposure and double slantwise holographic inscriptions, respectively.