It's an awfully important detail to completely omit from an article.
>Diffraction-limited focusing is demonstrated at wavelengths of 405, 532, and 660 nm with corresponding efficiencies of 86, 73, and 66%.
...but I'm not clear on whether that is from a single lens or if they constructed different lenses for each color. (Those wavelengths correspond to violet, green, and red light fwiw) EDIT: the full paper makes it clear this is three separate lenses, so yeah, you're right.
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G Bhttp://www.atmo.arizona.edu/students/courselinks/spring08/at...
There are thousands/millions¹ of separate visible light frequencies. Our eyes and brains takes that all in and does an enormously lossy mapping of that to 3 perceived colors.
If you only record 3 of those thousands/millions of frequencies, you will lose 99.9% of the light, and mostly make black photos.
¹ depending on how wide the frequency interval considered monochromatic is.
The filter approach is still used in most cameras (Bayer filters) but a vary narrow wavelength bandpass would not be appropriate for a consumer camera.
Actual LED lamps work around this issue by using phosphors to broaden the spectrum.
This quality of light is measured by the Color Rendering Index; the phenomenon of color differences due to narrowband light sources is known as metamerism.
The images displayed on a panel do not suffer this issue, because our eyes can detect only 3 "dimensions" of color; hence 3 narrowband illuminants suffice. (And in fact narrowband is necessary for a broad color gamut.) It is only when reflection/absorption comes into play that metamerism matters.
Cone cells have fairly peaked frequency responses, and due to random projections caused by the cascading, this is sufficient to fully reconstruct the signal, i.e. the converse of the statement is true, you can retain 99.9% of the perceptual information using 3 sensors, all you need is to perceive in time and some randomness in the sensor placement.
Maybe this example will clarify: Our eyes can not tell the difference between monochromatic green light (540nm) and a mix of blue (470nm) and yellow (580nm) light.
Your explanation of 'thousands of frequencies' is somewhere between misleading and incorrect. Electromagnetic radiation is a continuous frequency. Our eyes' 'sensors' are not sensitive to exact wavelengths of course, they are sensitive to a range. Some more sensitive to red, falling off into orange, into yellow, into green (as the frequency of light goes up). We are most sensitive to colors in the green spectrum, least sensitive to blue.
Do you know why the sky is blue? It is because of the spacing of ozone particles. It absorbs and reflects higher and lower wavelengths _more_ but red and green light still make it through, as well as UV radiation.
So blue is maybe 400-500nm, green 500-600nm and red 550-650mn.
But these new lenses only give sharp images in much narrower bands. If it has blue at 448-449nm, green 540-541nm and red 580-581nm, most of the spectrum will be lost.
You could get some image with single wavelength red, green, and blue sensors, and it might be pretty interesting looking, but it wouldn't see much like our eyes do.
For manufacturers but not for consumers, to an extent.
What about VR headsets? Flat lenses are good in that case, and you'd just have to manipulate 3 wavelengths.
Maybe close enough that it would work, but I'm also not sure whether you can do these metamaterial lenses for three wavelengths at once. If it's even possible, AFAIK it's not a solved problem.