The subject invention relates to the fabrication of micro-optical structures in a glass-like transparent material using conventional photolithography processing steps. The glass-like material is a spin-on glass (SOG) material, which behaves like a negative-tone photoresist, and has high quality optical properties similar to those of glass. The present invention can take advantage of gray scale photomasks to illuminate the uncured spin-on material with various illumination intensities, thus resulting in variations in resultant film thickness of the SOG material after the chemical development step. This results in micro-optical structures that can be fabricated with the desired shapes, depending on the transmission characteristics of each region of the gray scale photomask.