Thursday, April 08, 2021

One More Attempt of Holy Grail Color Router - Splitter

Canadian Western University, ON, publishes an iScience paper "Nanophotonic color splitters for high-efficiency imaging" by Eric Johlin.

  • Color splitters focus and sort light into pixels without any absorptive losses
  • New single-material splitters are designed to sit directly on a CMOS sensor surface
  • Splitters with four or more layers show significant improvements over filters
  • Color-corrected and nearly lossless greyscale imaging can be done with one splitter
Standard color imaging utilizes absorptive filter arrays to achieve spectral sensitivity. However, this leads to ∼2/3 of incident light being lost to filter absorption. Instead, splitting and redirecting light into spatially separated pixels avoids these absorptive losses. Herein we investigate the inverse design and performance of a new type of splitter which can be printed from a single material directly on top of a sensor surface and are compatible with 800 nm sensor pixels, thereby providing drop-in replacements for color filters. Two-dimensional structures with as few as four layers significantly improve fully color-corrected imaging performance over standard filters, with lower complexity. Being fully dielectric, these splitters additionally allow color-correction to be foregone, increasing the photon transmission efficiency to over 80%, even for sensors with fill-factors of 0.5. Performance further increases with fully 3D structures, improving light sensitivity in color-corrected imaging by a factor of 4 when compared to filters alone.

Graphical Abstract:


  1. One important issue with these beam splitters is the split efficiency under oblique incident light. There might be a lot of structures work great with normal incident light, but not many work well within a range of incident angle while many of these sensor applications are not restricted to collimated light.

  2. There seems to be a lot more color mixing than CFA. Wonder how that could impact the final image quality.


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