• light scattering
• nanoparticles
• optical filter

This thesis is part of a larger project devoted to understanding, modeling and realizing an optical system inspired by human vision. Precisely, this thesis is aimed at designing an electrically tuneable optical filter based on light scattering (within the visible spectrum) in order to mimic the foveal vision in human eyes.
The human vision system is highly dependent on the spatial frequency in sampling, coding, processing and understanding of how physical due to non-uniformity in the distribution of photoreceptors on the retina.
The small region, called fovea, has the greatest density of cones (they provide the eye’s colour sensitivity and are active at high light levels, i.e. photopic vision) and such distribution decreases toward the periphery. The rods density distribution is the opposite (they are responsible for vision at very low light levels, i.e. scotopic vision).
For this reason, the spatial resolution is not constant across our field of view, but is maximal at the fovea.
Our work is aimed at developing an optical filter tuneable, upon an electrically stimulus, and attenuate spatial frequencies before the photodetector sampling.
The idea is to have nano-particels with high density in pheriphery and decreasing them in the centre. This phenomenon allows to have a scattering of the light beam in correspondence of the peripheral sensors of a vision system (such as a camera), but not the central ones. So the effective maximal spatial frequency of the input is reduced before sampling.
This work is organised in a first experimental part and a second of software simulation. The software simulation has been developed in London in order to use Comsol Multiphysics and CST Studio Suite. The main steps followed are:
- Physical realization of different filters with different concentration of nano-particles
- Simple scattering analysis by measuring the resolution of images taken in the presence of the filters
- Software simulation to validate fundamental principles of scattering and to describe the filter behaviour.