Diffraction characteristics of surface-relief gratings.

We present a theoretical and experimental study on the diffraction characteristics of gratings, with particular attention focused on the effects of polarization. The goal of our study is to develop multifunctional devices for use in a pickup head for optical storage systems. Experiments and numerical calculations are carried out systematically to determine the effects of the grating parameters of depth, period, and duty cycle and also the effects of the incident-wave parameters of incident angle, wavelength, and polarization. It is shown that, theoretically, the diffraction efficiency can reach 100% for both TE and TM polarizations that are incident at the Bragg angle. The simple dispersion characteristics of the Floquet modes are invoked to explain the different diffraction behaviors between the two polarizations. We conclude that a suitably designed grating may split an incident light beam of mixed polarizations into two beams of the opposite polarizations, each propagating in a different direction. Based on the numerical results, simple criteria are suggested for the design of the grating structures for both polarizing and nonpolarizing beam splitters.