Time cloaking is possible because of a kind of duality between space and time in electromagnetic theory. In particular, the diffraction of a beam of light in space is mathematically equivalent to the temporal propagation of light through a dispersive medium. In other words, diffraction and dispersion are symmetric in spacetime.
That immediately leads to an interesting idea. Just as its easy to make a lens that focuses light in space using diffraction, so it is possible to use dispersion to make a lens that focuses in time.
Such a time-lens can be made using an electro-optic modulator, for example, and has a variety of familiar properties. “This time-lens can, for example, magnify or compress in time,” say Fridman and co.
This magnifying and compressing in time is important.
The trick to building a temporal cloak is to place two time-lenses in series and then send a beam of light through them. The first compresses the light in time while the second decompresses it again.
But this leaves a gap. For short period, there is a kind of hole in time in which any event is unrecorded.
So to an observer, the light coming out of the second time-lens appears undistorted, as if no event has occurred.
In effect, the space between the two lenses is a kind of spatio-temporal cloak that deletes changes that occur in short periods of time.