Directly fabricated multi-scale microlens arrays on a hydrophobic flat surface by a simple ink-jet printing technique

A shape-tunable approach is demonstrated for the fabrication of multi-scale polymer microlenses (mu-lenses) and microlens arrays (MLAs) using an ink-jet printing (IJP) technique. Also, the influence of the surface wetting conditions on the geometrical and optical characteristics of the printed mu-lenses is investigated. A photo-curable organic-inorganic hybrid polymeric resist (H-resist) is used; it is printed on a hydrophobic-treated glass substrate with different number of drops per mu-lens and cured using an ultraviolet lamp (UV lamp). High quality mu-lenses and MLAs with good uniformity and reproducibility were fabricated. The lens diameters and heights were controllable by changing the number of H-resist drops together with tuning the surface wetting conditions; these shape changes affect the optical properties of the mu-lenses and MLAs such as the numerical aperture (NA) and focal distance (f), as well as the f-number (f(#)), which indicates the light-gathering power. The optical properties of the tunable mu-lenses and MLAs are very attractive for application in optical systems such as interconnects and pixelated imagine sensors that use CCD or SPAD arrays, offering an efficient, simple and cheap alternative to the conventionally used photolithography technique.