SiO2-based diffractive/refractive hybrid microlenses were fabricated by using femtosecond laser-induced nonlinear
optical processes. Recently, hybrid devices have received much attention as important components for optical pickup
systems and integrated sensors. SiO2-based devices are particularly promising because of high transparency, physical and
chemical stabilities. For these devices, microfabrication upon nonplanar substrates such as convex lenses, which is
difficult for the semiconductor processes, is required. In this study, microFresnel lens patterns were directly written
inside positive-tone resists upon convex microlenses of 240 μm diameters by using femtosecond laser-induced nonlinear
absorption. The spot diameters are primarily determined at any position inside the resist by the region volume at which
the nonlinear absorption occurs. Therefore, the precise patterns could be formed even upon the nonplanar substrates.
After post-exposure-bake and development treatment, the patterns were transferred onto underlying lenses by CHF3
plasma. Here, the etching depth was 1 μm. Consequently, SiO2-based hybrid lenses with smooth surfaces were obtained. When He-Ne laser of 632.8 nm wavelength was coupled to this hybrid lens, the focal spot was 630 μm from the lens
surfaces. This focal length agreed with theoretical value of 618 μm. More functional optical devices would be realized
by improvement of fabrication processes.