Single and multi-array GRIN lenses from porous silicon

Intensive research for more than a decade has demonstrated that porous silicon (PSi) can be an excellent alternative material for multilayer optical devices, such as Bragg mirrors, microcavities and filters. In this paper, we shall describe a new application of PSi. We have designed, fabricated and tested various types of PSi based graded refractive index (GRIN) lenses. These planar micro-lenses are embedded in the Si wafer and have made-to-order focal lengths. Our fabrication technique allows the manufacture of a single lens or an array of lenses with variable focal length. The design opens the possibility of integrating the GRIN lenses with existing Si based optical devices such as detectors and waveguides.