Binary surface-relief gratings for array illumination in digital optics

Abstract

Separable binary-phase array illuminators for fan-out up to 1024 x 1024 and ~65% two-dimensional efficiency are designed by simulated annealing with constraints for maximizing the minimum feature size. A new nonseparable trapezoidal coding technique is introduced and applied to design high-efficiency (~75%-80%) array generators for fan-out up to 16 x 16. A rigorous electromagnetic diffraction theory is used to evaluate the range of validity of the scalar designs (both grating period and input angle are considered), to analyze fabrication errors (slanted groove walls and undercutting), and to design binary resonance-domain one-dimensional array generators with 90%-100% efficiency. Trapezoidal gratings for low fan-out (8 x 8), separable gratings for high fan-out (up to 128 x 128), and a 1 x 5 resonance domain (100% efficient) reflection grating are demonstrated experimentally.