Optical Entropy and Generalized Thermodynamics of Solitonic Event Horizons

Abstract: The realization of Hawking radiation in optical analogs has historically focused on kinematic observables, such as the effective temperature determined by the horizon's surface gravity. A complete thermodynamic description, however, necessitates a rigorous definition of entropy and irreversibility, which has remained elusive in Hamiltonian optical systems. In this work, we bridge this gap by introducing an operational entropy for solitonic event horizons, derived from the spectral partitioning of the optical field into coherent solitonic and incoherent radiative subsystems. We demonstrate that the emission of resonant radiation, mediated by the breaking of soliton integrability due to higher-order dispersion, serves as a fundamental mechanism for entropy production. Numerical simulations of the generalized nonlinear Schrodinger equation confirm that this process satisfies a generalized second law, where the change in total entropy is non-negative. These results establish optical event horizons as consistent nonequilibrium thermodynamic systems, offering a new pathway to explore the information-theoretic aspects of analog gravity in laboratory settings.