Broadening of Spectral Lines for Decaying Trapped States of Photonic Meta‐Atoms

ABSTRACT We study photonic meta‐atoms in nonlinear waveguides. They shed resonant radiation upon propagation, inspiring an analogy to radiative broadening in atomic spectra. Meta‐atoms consist of a soliton and weak trapped states, bound together by cross‐phase modulation. Higher‐order dispersion enables phase‐matching resonances that couple trapped states to the continuum, generating resonant radiation with a Lorentzian lineshape. We demonstrate that their linewidth follows from the finite lifetime of the corresponding trapped‐state and discuss prospects for observing the reported effect in photonic‐crystal fibres.