Controlled optical thermalization in quasiperiodic photonic lattices

A mechanism whereby a speed-up or slow-down of thermalization or prethermalization of multimode photonic lattices (measured by the propagation distance required for the system’s entropy to maximize) is proposed. The idea is to utilize the coexistence of extended and localized supermodes of lattices with mobility edge to prepare a wide range of input beams, which would cause the system to rapidly or slowly approach its equilibrium state. As a proof of concept, the generalized quasiperiodic Aubry–André potential is used to demonstrate such an accelerated-wind down “thermalization transition.” The underlying ideas are also extended to photonic lattices that lack energy-dependent mobility edge in their spectrum. By altering the original system (whose spectrum corresponds to only locally confined or widespread supermodes), the coexistence of localized and extended states is achieved in the new structure of the eigenvalues–coupling constant diagram while keeping the total power unchanged and the Hamiltonian nearly the same. In essence, the perturbation changes the localization properties of some supermodes from being extended to confined and vice versa.