Modulational instabilities in nonlinear optics are the fundamental processes that cause the transition from uniform states to structures in extended systems.Quite counterintuitively,such processes can be enhanced rather than inhibited when spectrally asymmetric losses are introduced into the system.In his fragment 76,the philosopher Heraclitus wrote“The death of earth is to become water,and the death of water is to become air,and the death of air is to become fire,and reversely”1.This sentence describes well the“identity of the opposites”,one of the most fruitful principles of dialectic thinking from ancient Greece to Hegel and beyond.These thoughts came to my mind when I read a recent paper by Perego and coworkers2,in which they show how in nonlinear optical systems,spectrally asymmetric losses can generate gain in the very same beam that is affected by losses.The death of losses is to become gain.
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