Fabrication of SiO₂hybrid microlens structures using femtosecond laser nonlinear lithography

Abstract

We fabricated three-dimensional SiO2 surfaces using femtoseond laser nonlinear optical lithography. By pattern transfers of polymerized resist patterns, which were written via nonlinear absorption, into underlying substrates, SiO2 hybrid microlens structures were created. Fresnel zone plate patterns were written on curved surfaces of microlenses whose diameters and curvature radii were 240 μm and 380 μm, respectively. The surface observation revealed that the surface roughness of the transferred SiO2 was improved with O2 concentration during plasma etching. When He-Ne laser light of 632.8 nm wavelength was coupled to the hybrid lenses, the focal lengths became shorter than those of the original refractive lenses. This shift amount of 216 μm was consistent with theoretical value of 213 μm, indicating nonlinear lithography was useful for the precise microfabrication of photonic devices with three-dimensional surfaces.