Cubic–quartic optical soliton perturbation with Fokas–Lenells equation by sine–Gordon equation approach

This paper recovers cubic–quartic optical solitons for perturbed Fokas–Lenells equation in polarization-preserving fibers and birefringent fibers. The perturbation terms appear with maximum permissible intensity. Singular and dark solitons, together with a few combo solitons, emerge from the sine–Gordon equation integration scheme.