Single-step fabrication of continuous surface relief micro-optical elements in hybrid sol-gel glass by laser direct writing

A negative tone hybrid sol-gel material was applied to the fabrication of continuous surface relief micro-optical elements by laser direct writing lithography. The hybrid sol-gel glass was synthesized as UV photosensitive material and used for the fabrication of micro-optical elements with continuous surface relief profile. The surface profile was directly controlled by the UV exposure dosage and the exposed areas were crosslinked and converted into sol-gel glass with relief structures. The UV exposure dosage was realized by an acousto-optic modulator (AOM) in the laser direct writing system. Characterization results indicated that the thickness of the sol-gel glass has a linear response to the AOM values ranging from 3.25 to 5.5. The sol-gel thin film was measured to have a refractive index of 1.52 and the maximum thickness of 2 μm. For various designs of diffractive optical elements within the visible wavelength, the sol-gel film enables us to achieve an arbitrary phase change between 0 and 2π with the linear AOM exposure range. As an example, a blazed grating with a period of 45 μm and height of 1.17 μm was fabricated in the sol-gel glass using direct laser writing method.