Study on optical gain from PCFs with active impurities

The characteristics of localized fields of doped photonic crystal fibers (PCFs) are studied by numerical simulation method in the paper. An interesting phenomenon is produced with the enhancement of stimulated radiation, which is the transmittivity being greater than one. And the numerical results show clearly the relation between the characteristics of localized fields, the abnormal group velocity in photonic band gaps and the negative imaginary component of the complex effective index of refraction of doped medium. Based on the relations the amplification of stimulated emission can be realized by introducing active impurities into the defect media of PCFs. Furthermore, the narrow transmission bands can be obtained by introducing line defects into the doped PCFs, which are used as channels in wavelength-division multiplexed (WDM) communication systems. And the doped PCFs can also be used to make optical amplifiers employed in dense WDM communication systems.