Tunable negative refraction in nematic liquid crystals

A tunable negative refraction mechanism based on the properties of nematic liquid crystals is proposed. It shows that negative group refraction occurs at the interface between air and the nematic liquid crystals, and that the refraction can be adjusted by an applied electric field and by the temperature. For a nematic liquid crystal (E7, Merck), the group refraction is negative for the voltages of 1.0-2.8 V and reaches a maximum at 1.5 V. The negative group refraction decreases monotonously with increasing temperature. Such mechanism demonstrates the feasibility of tunable negative refraction devices based on liquid crystals.