Surface relief micro-optical elements built in hybrid sol-gel glass

In micro-optical elements design, in order to achieve an optimal performance and reduce the undesired background optical system noise, multilevel phase-only micro-optical elements and/or continuous-relief structures are required. The multilevel and continuous relief structures can be fabricated by multiple exposures through a set of binary masks, electron-beam direct writing, laser-beam direct writing and grey scale masks. For mass production of cost-effective monolithic micro-optical elements, the high-energy beam-sensitive (HEBS) glass offers an opportunity to generate a grey-scale mask for analogue 3D surface relief structures. In this paper, a negative-tone inorganic-organic hybrid SiO2/TiO2 glass is investigated for the fabrication of refractive and diffractive micro-optical elements. The sol-gel material enjoys an advantage over the conventional photoresist based fabrication techniques due to its single step etching-free process.