Nanophotonic Color Image Splitters

Background

Digital color imaging is a ubiquitous technological process that relies on the combination of responses from distinct red, green, and blue pixels to produce full color images. This color sensitivity is achieved by color filters absorbing light of all colors other than the one being imaged by a given red, green, or blue pixel (Figure 1a). This absorption however limits the efficiency of the sensor to less than 33%, just from the colour filter alone. The significant losses are becoming an increasing issue, particularly when image sensors are becoming smaller, higher resolution and need more efficient sorting of light.

Technology Overview

Researchers at Western University have developed color splitters that aim to remove this source of absorption loss. Instead of absorbing incoming light, the color splitters allow for the proper color light to be redirected into the corresponding pixel, thereby allowing a theoretical tripling of light collection efficiency (). These novel splitters are expected to serve as simple drop-in replacements for current absorptive filters.

More recently, as of April 2024, prototype development of the color splitters is underway and there are promising absorption results for both single layer (2D) structures developed by traditional electron beam lithography, as well as stacked two-layer splitter printed using a two-photon lithography system. Focusing of light at the center of the pixel regions is visible, and separation into the three color bands is present (). It is anticipated that even higher performance and absorption efficiency can be achieved with refinements of the designs and processes, as well as multi layered splitters and prototypes of these structures are under development.

Further Details:

https://www.sciencedirect.com/science/article/pii/S2589004221002364

Benefits

The main benefit of this invention includes dramatically increasing the light absorption efficiency of the sensors. This increase in efficiency can allow for smaller pixel sizes, higher sensitivity imaging in cameras, and additional color channels to be detected (multi-spectral imaging). This can allow companies to offer higher quality imaging in both as a capital goods and consumer products. Other benefits are described below:

• 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 and low-light vision applications, 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 or imprint lithography (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 as low as 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

Applications

• Biological imaging
• Machine vision
• Smart sensing materials
• Real-time motion detection
• High resolution imaging
• Space based applications – i.e. Aerospace imaging
• Defense applications ‑ low-light (night) vision

Opportunity

Western University are also looking for development and commercial partners.