DESIGN CONSIDERATIONS OF FORM BIREFRINGENT MICROSTRUCTURES

Diffraction characteristics of high-spatial-frequency (HSF) gratings a re evaluated for application to polarization-selective computer-genera ted holograms by the use of two different approaches: second-order eff ective-medium theory (EMT) and rigorous coupled-wave analysis (RCWA). The reflectivities and the phase differences for TE- and TM-polarized waves are investigated in terms of various input parameters, and resul ts obtained with second-order EMT and RCWA are compared. It is shown t hat although the reflection characteristics can be accurately modeled with the second-order EMT, the phase difference created by form birefr ingence for TE- and TM-polarized waves requires the use of a more rigo rous, RCWA approach. The design of HSF gratings in terms of their form birefringence and reflectivity properties is discussed in conjunction with polarization-selective computer-generated holograms. A specific design optimization example furnishes a grating profile that provides a trade-off between the largest form birefringence and the lowest refl ectivities.