Comparison of gain dependence of different Er-doped fiber structures

The dependence of gain in Erdoped fibre on Vvalue refractive index dip confinement of Er atoms and diffusion at the core cladding interface is presented. The absorption of the pump light and the gain of the signal light are calculated by solving the population density equations as a function of radial and axial position in the fibre. When the pump wavelength is 980 nm the optimum Vvalue at signal wavelength 1530 nm of a step index fibre increases from 1. 16 to 1. 29 with the pump power increasing from 2 mW to 8 mW. When the pump wavelength is 1490 nm the optimum Vvalue is 1. 37 without pump power dependence. With the confinement of the dopant atoms the gain can be improved as much as 68 . The confinement increases the optimum Vvalue to around 1 . 44. The gain is decreased 37 by an index dip which is 75 of the core diameter and 100 of the index difference. The diffusion of the dopants at the interface between the core and the cladding decreases the calculated gain 17 when the core radius increases 40 due to the diffusion measured at 10 index difference level.