In this paper, we present a comprehensive mathematical model for the novel double cladding fiber, based on the rate and propagation equations, the output signal power and noise characteristics of double-cladding erbium-ytterbium co-doped fiber amplifiers with a reflector are analyzed numerically. Due to the contributions of the reflector to reflect the un-absorbed pump power, pump light transmitted in the active fiber is increased and the output performances are improved, it is shown that the amplifiers with the reflector have about the same high-power output signal as those without it, only using half-lengths of fiber. The pumping scheme and numerical results could be useful for the real optimized design of DCF amplifier in the near future.
In order to achieve higher output powers, double-clad fibers (DCF's) are widely used by optical fiber lasers and amplifiers. In this paper, we present a comprehensive mathematical model for the novel multi-mode (MM) double-clad (DC) Er: Yb co-doped hexagonal fiber, Based on the rate and propagation equations, the pump light and forward and backward-amplified spontaneous emissions (ASE±) light transmission in the fiber are analyzed numerically and measured. The simulative and experimental results show that pump power was absorbed almost completely when the length of the fiber is about 3.5~4 m, the suitable length of the fiber in optical fiber lasers is 2~2.5 m. and the 2 m long fiber emits at 1535 and 1543 nm simultaneously, and the peak-value wavelength of ASE+ changes to the long wavelength with the increase of the pump power. The results investigated are useful for the design of optical fiber lasers.