Miniaturized porous silicon rugate filter wheel for multispectral imaging applications

Porous silicon has attracted the attention of material research during the past two decades due to its efficient visible luminesce and fascinating passive optical properties. By controlling of pore size and pore density, different optical properties are determined, which cane offer a wide range of applications in many fields, from optical devices to chemical sensors and biomaterials. In this paper, a novel approach for generation of a miniaturized porous silicon based rugate filter wheel with nine different filter segments in the MIR wavelength range suitable for portable multispectral imaging systems is presented. The filter wheel segments are patterned on a silicon wafer using silicon nitride insulating masks and generated using the anodization technique. Specific characteristics of the filter segments are adjusted by "the current squeezing effect" during the anodization through the geometrical size of the filter segments, which results in local current redistributions and consequently different porous silicon formation rate and porosity in the wheel elements.