Western University Background
Color imaging is most commonly achieved through absorptive Bayer filter arrays, with each of the three color pixel filters allowing approximately 1/3 of the incident light to transmit to the active material below. While this allows high selectivity of indicial colors and thus simple image processing, the significant losses are becoming an increasing issue, particularly as the trend toward smaller, higher resolution sensors further reduces the incoming average photons count per pixel.
A researcher at Western University has developed a computational process that provides a method of color imaging that does not rely on absorptive filter arrays.
The splitters both remove the need for micro lens arrays to focus light on active regions (remove losses from color filters by factors of 2to4, depending on configuration), and remove the need for a second sensor to perform high sensitivity grayscale imaging. The stated benefits include increased sensitivity since filters typically attenuate up to 2/3 of incident light. It is designed to determine geometric shapes and structures that succeed at splitting the broadband, randomly (or linearly) polarized light into the desired pixel array (400-500nm blue, 500-600nm green and 600-700nm red). These developed structures range from single-layer meta-surfaces to fully 3D photonic-crystal-like structures, both of fully dielectric materials.
This method will allow this novel splitters to serve as simple drop in replacements for current absorptive filters, which significantly increasing sensor transmissivity.
High Efficiency/Exceptional Performance – significantly surpasses collection efficiency of traditional filter arrays for splitter designs even with as few as four layers, with efficiency enhancements as high as 4 times over CMOS sensors without micro-lens arrays- offer particular advantages in color biological imaging, where high efficiency, small pixel sizes, and color sensitivity are all desired
Nearly Lossless Grayscale Imaging – splitter structures show added functionality in the ability to choose any point in the color accuracy vs. sensitivity trade-off permitting accurate color imaging, nearly lossless grayscale imaging, and anything in between, all on the same sensor.
Easy Development – the structures are fabricable through either sequential photolithography (for layered structures) or printed directly with multi-photon lithography, and are printed directly on a sensor surface.
Simplicity – do not require any focusing micro-lens arrays, even when used with CMOS sensor configurations with active area fractions of 50%, further simplifying the use of such components.
Robustness – splitter operation does not rely on changing the angular distribution of light, allowing high performance from off-angle illumination, and with any degree of light polarization
Tunability – design optimization can be performed for any pixel size, spectral regions of interest, or overall thickness desired for a particular application
Smart sensing materials
Real-time motion detection
High resolution imaging
Space based applications – i.e. Aerospace imaging
Western University are also looking into development partners to validate the model in Space-based applications (aerospace imaging for high performance and sensitivity), as well as
Controlled Environment (e.g. looking at fluorescence imaging of biological samples where a spectrum is already known but color images are still useful)
Uncontrolled Environments (e.g. consumer camera sensors, where there is no known spectrum ahead of time)