Disclaimer: This informal post assumes you are familiar with basic photonics and applied chaos theory.
Unfortunately, “chaos” has become a buzz word. Instead of using chaos as an umbrella term, I will use chaos to mean chaotic parameter driving (because that’s the cool stuff)! There is synchronized chaos.
Lasers are nonlinear oscillators – their behavior can be periodic or chaotic. You can sync two lasers operating in a chaotic state!
If we place two lasers such that their beams are parallel and separated by a small distance $dx$, the beams themselves will not overlap. For a small enough $dx$, their electric fields do! This direct physical coupling of the two lasers is enough to induce sync!
You can also sync a bunch of different electronic circuits with linear error feedback coupling. Chua’s circuit is a freaking sweet combination of a chaotic electronic circuit and an optoelectronic chaotic oscillator. You can couple Chua’s circuit with a plasma discharge tube (Chua’s circuit produces the HV DC current require to power/sync with the discharge tube). Even though the systems are physically different they couple anyway! And that, my friends, is a wonderful demonstration of the beauty of math.