Low numerical aperture refractive microlenses in fused silica
Fused silica microlenses with low numerical apertures (NAs) were fabricated. The original photoresist element was realized by the melting resist technology and was transferred into fused silica by reactive ion etching. Low selectivity etching was applied to realize the low NA microlenses. An etch selectivity between photoresist and fused silica down to 0.1 was achieved by using SF6 and O2 gases. Refractive microlenses with NAs down to 0.018 were obtained.