A serial of LC gratings are fabricated mainly based on photoalignment, which include (1) Nematic LC grating with alternating 90° twisted nematic (TN) regions and homogeneous alignment (PA). Both 1D and 2D diffraction gratings are demonstrated by periodic photoalignment of sulfonic azo-dye (SD1) films with a linearly polarized light beam. (2) A polarization independent of 1D/2D LC gratings with alternate orthogonal homogeneously aligned regions. No polarizer is employed. (3) A polarizer-free submillisecond response grating employing dual-frequency LC (DFLC) together with patterned hybrid aligned nematic (HAN) structures. To obtain instantly controllable LC microstructures rather than simple gratings, a digital micro-mirror device (DMD) based a micro-lithography system is developed. It may generate arbitrary micro-images on photoalignment layers. Besides normal phase gratings, more complex 2D patterns including quasicrystal structure are demonstrated, which give us more freedom to develop microstructured LC based photonic devices.
Some of our recent progress on liquid crystal (LC) gratings, from nematic to blue phase, is reviewed in this invited talk.
The first kind of grating is fabricated by periodically adjusting the LC directors to form alternate micro phase retarders
and polarization rotators in a cell placed between crossed polarizers. The second one is demonstrated by means of
photoalignment technique with alternate orthogonal homogeneously-aligned domains. To improve the response time of
the gratings, several approaches are also proposed by using dual-frequency addressed nematic LC, ferroelectric LC and
blue phase LC, which shows great performance including high transmittance, polarization independency and
submillisecond response. At last, to obtain other controllable LC microstructures rather than simple 1D/2D gratings, we
develop a micro-lithography system with a digital micro-mirror device as dynamic mask forms. It may instantly generate
arbitrary micro-images on photoalignment layers and further guides the LC molecule orientations. Besides normal phase
gratings, more complex patterns such as quasicrystal structures are demonstrated. Some new applications such as tunable
multiport optical switching and vector beam generations are expected.