The idea of optical cloaking, or more generally the concept of invisibility, has gone from science fiction trope to serious topic of physics research to subfield of optical science in its own right in a remarkably short period of time.
One of the most fascinating aspects of the “cloaking craze,” as I have referred to it before, is that the optics of cloaks and the mathematics used to design them have implications far beyond the simple idea of hiding an object. Lessons learned from cloaking have been used to design such exotic devices as “perfect” lenses, space-time cloaks, and optical black holes. The number of ingenious applications has been growing at a rapid pace (although most are still purely theoretical), and others almost certainly still wait to be discovered.
Of all the ideas suggested, my favorite is one that has gotten relatively little attention: the ability to make “perfect” optical illusions. In principle, it is possible to wrap an object in an illusion cloak to make that object look like a completely different one. A simple illustration of the idea is shown below, in which an apple is surrounded by a cloak that makes it look exactly like an orange.
It is important to realize that this illusion is three-dimensional: the apple ends up looking like an orange from all directions of observation. The disguise is far more complex and effective than simply draping the apple in a tarp with a picture of an orange on it!
This surprising trick is an inevitable consequence of the existence of (theoretically) perfect invisibility cloaks, and in turn it leads to even more surprising possibilities! In this post we look at how such illusions are possible, and what implications they have for future optical devices.
Skulls in the Stars 
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