Direct laser writing of tunable diffractive micro-optics on graphene oxide film

Abstract

In this study, we present diffractive optical elements printed on reduced graphene oxide (rGO) thin film using a femtosecond (fs) laser as the direct laser writing source. Graphene oxide (GO) is an interesting optical material providing unique properties such as the large light absorption modulation level during its laser reduction process; after the photoreduction, the transparent GO become opaque rGO. In order to fabricate the diffractive optical pattern of GO and rGO with sub-micrometer resolution, we use femtosecond laser pulses to induce the photoreduction of GO resulting in the ultrathin binary diffractive optical elements such as a light diffraction grating and a Fresnel lens. In addition, the rGO can play a role as a complaint electrode so that the rGO pattern can be applied to a dielectric elastomer actuation (DEA) after the pattern is transferred to a dielectric elastomer substrate with the few tens of micrometer thickness. As a high voltage is applied to the flexible substrate, it can be stretched, which leads to the expansion of the diffractive element; it means the light diffraction pattern of the element can be tunable as well. Therefore, we could control the optical specifications of the elements, such as grating period and the focal length of the Fresnel lens. Because of the simple fabrication process and arbitrary patterning capability of the femtosecond laser direct writing will provide ultrathin, tunable, compact, cost-effective, and highly efficient optical components over conventional optics.