Study on the Optical Gain of Photonic Crystals Fiber with Active Impurity

Basing on the theory of spontaneous emission from two-level atoms in photonic crystal fibers(PCFs),we demonstrated the inevitable existence of localized fields of defect modes as well as their basic properties.It provides theoretical proof for inevstingating into the inherent laws of spontaneous radiation from doped media.On the basis,the relation between the enhancement of stimulated emission as well as transmissivity being greater than one and the abnormal group velocity in photonic band gaps as well as negative imaginary part of the complex effective index of refraction of doped defect layer is studied by numerical simulation method.Therefore great amplification of stimulated emission is obtainablel.