Reprogrammable diffractive micro-optical elements

Abstract

The fabrication of Diffractive Optical Elements (DOEs) involves the structuration of material surfaces with geometries on the scale of light wavelength. Differently to standard photoresists, thin films of amorphous azobenzene-containing polymers (azopolymers) directly develop surface reliefs in the irradiated area, directly usable as phase-modulating masks, acting as DOEs. Surface structuration is the result of an intrinsically reversible light-induced material displacement, which makes azopolymer films usable as photo-transformable planar diffractive optical devices. Here we demonstrate reprogrammable and ready-to-use diffractive gratings, lenses, and holographic projectors, directly obtained in a single photo-structuration step through the projection of a grayscale holographic pattern over the azopolymer film free surface. The all-optical scheme, based on the principles of computer-generated holography, allows a simple and accurate engineering of the light pattern used for the azopolymer surface structuration. Additionally, direct pattern transferring opens to the real-time optimization of the device allowing to test and prototype its diffraction properties right during the developing of structured surfaces. The proposed approach offers a versatile, efficient, and full-optical reversible fabrication framework for DOEs, making it a promising option to overcome the demanding, burdensome, and irreversible manufacturing processes typically involved in the realization of planar diffractive optical devices.