A tilted bilayer membrane, which consists of two thin films of transparent optically isotropic materials of different refractive indices, can function as a transmission quarter-wave retarder (QWR) at a high angle of incidence. A specific design using a cryolite-Si membrane in the infrared is presented, and its tolerances to small shifts of wavelength, incidence angle, and film thickness errors are discussed. Some designs provide a dual QWR in transmission and reflection. Such devices provide simple linear-to-circular (and circular-to-linear) polarization transformers. Bilayer eighth-wave retarders without diattenuation are also introduced.
Journal of the Optical Society of America A
R. M. A. Azzam and Fadi A. Mahmoud, "Tilted bilayer membranes as simple transmission quarter-wave retardation plates," J. Opt. Soc. Am. A 18, 421-425 (2001)