Low cost production of computer-generated holograms: from design to optical evaluation

Abstract

In this work we review some optical characterization methods useful for the low cost production of two phase level computer generated holograms (CGH). As an example, binary CGH are designed with an iterative Fourier transform algorithm (IFTA) and fabricated on a silicon master micromachining with a single step of selective dry etch of silicon dioxide (SiO2) layer. The CGH characterization is performed in three steps; a first one involves the application of spectroscopic ellipsometry measurements to accurately measure the thickness of the SiO2 layer. These results permit the evaluation of the relative complex reflectance between the two levels of the developed hologram as a function of the wavelength. In a second step, interference microscopy is applied to directly visualize the phase shift in the SiO2/Si binary phase profile. Finally, the performance and diffraction efficiency of the fabricated CGH is compared for various lasers with different wavelengths. These experimental measurements in these two last steps confirm with very good accuracy the results derived from the spectroscopic ellipsometry analysis. In conjunction, the combination of these well established optical techniques provides a precise optical characterization of binary diffractive optical elements produced with simple and low cost technique, useful for mass production.