Coherence and Polarization Effects of Light Diffraction by Microlens Arrays

Influence of incident light beam coherence on the uniformity in the intensity distribution of diffracted beam by microlens array is investigated. Optical efficiency is calculated for different polarizations. It is shown that the intensity profile and radiation pattern of LED source beam diffracted by periodic micro-lens array are highly uniform and insensitive to the wavelength of incident beam. The spreading angle and output efficiency of the diffracted beam is more sensitive to the aspect ratio of microlens array (MLA). The bigger aspect ratio the higher spreading angle and lower the output efficiency. For a given spreading angle the aspect ratio can be decreased substantially if high-index material is used. Significant influence of wave-front curvature and polarization of incident beam on the reflectance and transmittance is shown.