Liquid crystals play an important role in the modern technologies because of their unique physical and optical properties. In addition to the most common application of the liquid crystal technology in liquid crystal displays (LCDs), a wide range of applications have been found, such as in photonics. In this thesis, liquid crystal polarization gratings with spatially varying birefringence distribution have been studied both theoretically and experimentally.

Firstly, the fabrication of different types of polarization gratings was discussed. The spatially varying pattern on an alignment material was achieved through polarization holography and photo-alignment technology. Defect free pattern was obtained with grating pitch as small as 2μm. The optimized retardation value with f...[ Read more ]

Liquid crystals play an important role in the modern technologies because of their unique physical and optical properties. In addition to the most common application of the liquid crystal technology in liquid crystal displays (LCDs), a wide range of applications have been found, such as in photonics. In this thesis, liquid crystal polarization gratings with spatially varying birefringence distribution have been studied both theoretically and experimentally.

Firstly, the fabrication of different types of polarization gratings was discussed. The spatially varying pattern on an alignment material was achieved through polarization holography and photo-alignment technology. Defect free pattern was obtained with grating pitch as small as 2μm. The optimized retardation value with film thickness over critical thickness was achieved by multilayer spin coating technique. Complex type polarization gratings were also fabricated through additional chiral doping into polymeric liquid crystals.

Then, a fast and accurate method based on extended Jones matrix has been proposed to characterize the properties of polarization gratings at oblique incidence. The transmitted field of a wave passing through a polarization grating at various incident directions was described by a spatially varying extended Jones matrix. The far field diffraction properties of the m^th order of the grating were determined by vectorial Fourier coefficients of the transmitted field. Therefore, the polarization state of the m^th order diffraction was fully characterized by a 2×2 matrix. The experimental results showed very good agreement with the calculated data for both primary type of polarization gratings and complex type of polarization gratings.

After thoroughly characterizing various types of polarization gratings, we further optimized configurations of polarization gratings according to different applications. We proposed to apply a polarization grating to a projection system based on Color Filter Liquid Crystal on Silicon (CF_LCOS) technology. A polarization grating combining CF_LCOS projection system using white light LED as light source was demonstrated. The un-polarized light coming out from LED was utilized and modulated directly. The overall system efficiency can be increased by 100% potentially. The simulation results showed that above 400:1 system contrast ratio can be achieved at F/2.2.

We also proposed the polarization gratings for beam steering applications. A wide viewing angle polarization grating was designed for multi-stage beam steering system. A simplified model was developed to characterize the polarization gratings at off-axis. The calculation speed was dramatically increased. Through the super-fast algorithm, a wide viewing angle polarization grating, which has suppressed 0^th order leakage at a wide incident angle range, was achieved through the parameter space approach.