We describe a broadband achromatic half-wave retarder for normally incident light of arbitrary polarization. The device consists of a stack of one nematic liquid-crystal cell with uniform alignment sandwiched between two twisted nematic layers that have identical twist angles (135°) but different orientations of their surface alignment. As a specific application, for light with linear polarization at 45° to the optic axis of the homogeneous cell the stack functions efficiently as an optical switch. The switch rotates the incident linear polarization by 90° in the absence of an electric field. When sufficiently high voltage is applied to all three layers, the device produces a near-zero effect on the incident polarization. An achromatic response in the spectral range 400–700 nm is achieved for both activated and quiescent states.
© 2004 Optical Society of America
M. D. Lavrentovich, T. A. Sergan, and J. R. Kelly, "Switchable broadband achromatic half-wave plate with nematic liquid crystals," Opt. Lett. 29, 1411-1413 (2004)