  Due to its high electrical conductivity and excellent transmittance at
terahertz frequencies, graphene is a promising candidate as transparent
electrodes for terahertz devices. We demonstrate a liquid crystal based
terahertz phase shifter with the graphene films as transparent electrodes. The
maximum phase shift is 10.8 degree and the saturation voltage is 5 V with a 50
um liquid crystal cell. The transmittance at terahertz frequencies and
electrical conductivity depending on the number of graphene layer are also
investigated. The proposed phase shifter provides a continuous tunability,
fully electrical controllability, and low DC voltage operation.
