Spectrally selective fundamental core mode suppression in an optical fiber with absorbing rods

In this paper, we demonstrate the spectrally selective fundamental core mode suppression in single-mode fiber by mode anti-crossing technique. A unique feature of the method proposed in the current work is that the fundamental core mode can have rectangular-like excess loss spectrum with bandwidth controllable by fiber bending. This property made the proposed fiber design to be promising for suppression of lasing at unwanted wavelengths in different fiber lasers and amplifiers.