The human retina consists of two major image processing regions: the fovea and the peripheries. The fovea provides acute vision. Optical signals collected by foveal receptors are transferred to the visual cortex through neurons in the ratio of almost one neuron per one receptor, providing high spatial resolution. In contrast, the retinal peripheries spread from parafovea to regions farther than 90° from the optical axes of the eye. The peripheries are constructed of receptive fields in which clusters of receptors are connected through a few functional layers with a neuron transmitting optical signals to the brain. Receptive fields in parafoveal zone count a few receptors per neuron. In the far peripheries, receptive fields can have several thousands of receptors passing preprocessed optical information to the brain through a single neuron. Receptive fields perform many functions absent in the fovea. One of these functions is motion detection. Another is brightness integration through which the total amount of light reaching a particular receptive field is converted to the signal amplitude in the respective neuron. In order to provide the described functions of receptive fields with the additional limitation on processing power, a photonic solution has been proposed utilizing the properties of photoluminescent concentrators. A stacked, three layer, structure was designed and fabricated. Each photoluminescent concentrator layer was responsible for detecting one prime colour, respectively, from the projected image. Layers were made of PMMA (polymethyl methacrilate) with embedded photoluminescent agents. The agents used were Sulphorodamine 101 for red, Rhodamine 6G for green, and Coumarin 6 for blue colour. Circumferences of circular concentrator layers were coupled with planar, ring shaped, coaxial photodiodes fabricated on a Si substrate. Finally an electronic circuit was designed to switch from color vision to B&W vision at low illumination levels by bridging primaries to increase the brightness sensitivity by a factor of approximately 3.
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