Voltage-controlled liquid-crystal terahertz phase shifter and quarter-wave plate

Phase shift exceeding pi/2 at 1 THz is demonstrated by using electrically controlled birefringence in a homeotropically aligned nematic liquid crystal (E7) cell, 570 mu m in thickness. The driving voltage required for a phase shift of 90 degrees is 125 V (rms). We demonstrate that the phase shifter works as an electrically switchable quarter-wave plate at I THz. The device can also be used as an electrically tuned phase compensator around the quarter-wave point near 1 THz. (c) 2006 Optical Society of America.