Revolutionary ‘Spaceplate’ Could Eliminate Traditional Camera Lenses

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patta
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Re: Revolutionary ‘Spaceplate’ Could Eliminate Traditional Camera Lenses

Post by patta »

Hmm, at first read it sounds bit as a joke. Always beware of articles about "revolutionary" technologies. Nature Communications seems to be specialized in publishing bombastic titles and abstracts - while the substance is more like routine research; maybe sometime a nice hint. Then, journalists pick just the title and build marvelous fantasies from it. We all like to be amazed.

Of course, if we have a magic Spaceplate that compresses space, we could make lenses smaller. Thanks. If we have a magic Spaceplane, we could fly to the moon every weekend. If we have a magic objective with high NA and infinite depth of field, we could ditch stacking. If....
Did they found a new way to compress space, did they manufacture such Spaceplate? No.

The main experiment actually performed was to put an air gap (a barrel full of air, sealed by two glass flats at the ends) into a cup of oil.
Air has lower refractive index than the oil, so, yes, the air barrel shortens the focal length of a lens, compared to the focal length in oil. Woooha! This unprecedented discovery is then presented as a proof-of-concept for the Spaceplate revolutionary technology. Seriously. Optical designers use this trick since 2 centuries, they call it "air lens"; air has lower refractive index than glass, so it "compresses space". An "air lens" is the high-tech, revolutionary spacing between two glass lenses.
A bit more sophisticate in the paper is the use of a "negative birefrengent" material, but again, use of birefrengent materials have been thoroughly explored since 2+ centuries. Birefrengent materials have been banned from imaging optics because of the too many side issues. And no current birefrengent material can compress the light path more than... air.

Much more interesting, this "light compressor" may be manufactured with metamaterials, which is the specialization of the paper authors. We can say that it is a "flat metalens" (Woooha!). It may compress the light path much more than air/vacuum, thus allowing to make much shorter optical systems. Did they fabricate it? No. They proposed a design made of layers; the concept appears to be similar (if not identical) to multilayer antireflection coating. The design is done by a generic AI search algorithm, with no discussion whatsoever of how, and on which principles, the compression of light waves is achieved. There is a digression about causality... but the brick and mortar? Metamaterials are radio antennas on small scale, not Black Holes. Then to conclude, this Spaceplate is difficult to calculate and design; and (my guesses) will be a nightmare to manufacture; works only for one wavelength; only near axis and at small NA; only with long spatial coherence (lasers).

Does this idea of Metamaterial Light Compressor have a future? Maybe, if somebody sit down, study it properly and manage to manufacture it, despite all odds. Maybe the authors of the paper have already a decently working design, but decided to keep it confidential until mature, and published a trimmed-down report to pitch attention.
Is this idea new? Not sure, let's read Newton, Huygens or Rayleigh and see if they've already discussed it. Which is highly probable.

After all, the paper is quite good, well written and detailed; but expect no miracles.

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