Graded refractive index devices from porous silicon

This paper discusses a number of optical devices that fabricated from mesoporous silicon to highlight the excellent device qualities and ease of fabrication which is achievable using PSi. Specifically, the paper discusses about the design and properties of devices with continuously varying refractive index profiles. The authors have made two types of index gradients: axial gradients, in which the index varies parallel to the optical axis, and radial gradients, in which the index varies perpendicular to the optical axis. As an example of axial gradient device, the authors discussed the design and fabrication of rugate filters with sinusoidally varying refractive indexes that act as single line reflection filters with narrow line-widths (< 10nm) and close to 100% reflectivity. The authors also talk about gradient refractive index (GRIN) lenses that we made for the first time from PSi. These planar lenses are embedded in the Si wafer and have, in theory, the ability to correct chromatic and some other aberrations that afflict conventional lenses.