Currently, the liquid crystal molecules generally include two types, namely rod-like crystal molecules and discotic liquid crystal molecules.  The orientation of a liquid crystal molecule is defined by the relationship between its direction vector and the substrate of a liquid crystal display (LCD).  The molecule alignment of rod-like liquid crystal molecules is illustrated in FIG.  1; the rod-like liquid crystal molecules in FIG.  1 (a) are horizontally oriented, while the rod-like liquid crystal molecules in FIG.  1 (b) are vertically oriented.  The direction vector of a rod-like liquid crystal molecule is defined as the long axial direction.  The molecule alignment of discotic liquid crystal molecules with a uniform orientation is illustrated in FIG.  2; the discotic liquid crystal molecules in FIG.  2(a) are vertically oriented, and the discotic liquid crystal molecules in FIG.  2 (b) are horizontally oriented.  The direction vector of a discotic liquid crystal molecule is defined as the direction perpendicular to the disc surface.  Usually, the direction of the orientation of a liquid crystal molecule is defined by the relationship between the direction of the substrate and the direction vector of the liquid crystal molecule.  If the direction vector of a discotic liquid crystal molecule is perpendicular to the substrate, its molecule alignment is a vertical orientation of the discotic liquid crystal molecule; and if the direction vector of a discotic liquid crystal molecule is parallel to the substrate, its molecule alignment is a horizontal orientation of the discotic liquid crystal molecule. 
Usually, the uniform orientation of discotic liquid crystal molecules can be achieved by techniques such as surface modification, polarization light alignment treatment, electric/magnetic field alignment treatment, mechanical rubbing, zone melting process, or the like.  These alignment techniques are usually limited by factors such as high requirements on the equipment or light source, complicated processing, or the like.  For the more complicated hybrid alignment of discotic liquid crystal molecules, often two or more alignment techniques need to be applied in combination, which therefore requires more complicated process or molecule design for the alignment agent.  These factors have limited the research and application of the optical functions of the discotic liquid crystal.