Generating electrically tunable optical vortices by a liquid crystal cell with patterned electrode

An electrically tunable optical vortex was generated in an antiparallel liquid crystal cell, where one electrode was patterned by a photomask, which is achieved by transferring a computer-generated hologram onto a transparency with a resolution of about $25μm$⁠. When a voltage was applied on the cell, an index modulation was induced due to the realignment of liquid crystal molecules, and then an optical vortex beam was produced. The diffraction efficiency measured was about 27.5%. The device also showed a reasonably fast response time.