Deposition of optical microlens arrays by ink-jet processes

Abstract

Ink-jet processes using either a drop-on-demand or a dosing system have been applied to the deposition of single lenses and large arrays of high optical property refractive microlenses. The lenses are made of a silica based inorganic-organic material which can be densified either thermally or by UV irradiation at low temperature. Microlense diameter d and height h made with a single drop can be varied between approximately d=50 µm and 2 mm, and h=6.25 and 150 µm, respectively, conferring a focal distance varying between 100 µm and approximately 10 mm, respectively. Large arrays of lenses have been realized with a minimum separation between the lenses as small as 5% of their diameter. Single lenses and arrays of lenses made with multidrops were also obtained. Microdrops (1000) with d=50 µm allow us to obtain lenses with diameter 800 µm, height 56 µm and focal distance of 2.9 mm. All the components have a high optical transparency (92%) within the wavelength range 300 nm-2.7 µm, are highly homogeneous and have very low stress and astigmatism. The index of refraction can be tailored by modifying the sol composition. The lens average surface roughness is Ra≈40 nm. Their shape measured by profilometry and their focusing properties, determined in and near the focal plane, are reported.