General insight into the complementary medium-based camouflage devices from Fourier optics.

We present a general insight into complementary medium-based camouflage devices from Fourier optics. The cloaks are simply spatial filters with different transfer functions and play the role of passively remedying or actively modulating the propagation optical field to make an object invisible or changeable. We further analytically show and numerically demonstrate two filters for realizing another invisibility method: optically camouflaging an object at one place to appear at another place with parallel displacement or orientation changeable displacement, respectively. Our analysis is from a completely different point of view and should clarify understanding of the mechanism of invisibility phenomena.