Porous silicon based rugate filters are emerging as interesting functionalized optical components in Micro-Opto-Electro-Mechanical Systems due to their specific nanostructures and superior optical properties. In this work, a cost-effective approach to generate a porous silicon based rugate filter wheel containing nine filter segments in the visible wavelength range suitable for 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 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 porous silicon formation rate and porosity modifications. A finite element model made in COMSOL Multiphysics is also presented to study redistributions of the current density and the current squeezing effect during the anodization for the proposed filter wheel. The proposed filter wheel can be miniaturized and integrated into a portable multispectral imaging system.
Keshavarzi, S., Kovacs, A., Abdo, M., Badilita, V., Zhu, R., Korvink, J. G., & Mescheder, U. (2019). Porous Silicon Based Rugate Filter Wheel for Multispectral Imaging Applications. ECS Journal of Solid State Science and Technology, 8(3), Q43–Q49. https://doi.org/10.1149/2.0251902jss