Longitudinal cascaded few mode erbium-doped fibers using PSO method with ultra-low differential modal gain

In this paper, we propose a longitudinal cascaded few-mode erbium-doped fiber amplifier (FM-EDFA) by particle swarm optimization (PSO). Triple-cascaded few-mode erbium-doped fibers (FM-EDFs) are applied longitudinally, which have the same refractive index distributions and different erbium-ion doping profiles. Each fiber is uniformly doped in different regions. The input power of the pump and signal are settled. The length and order of three pieces of FM-EDFs are optimized by PSO, which helps to minimize the differential modal gain (DMG) and maximize the modal gain at the output port. An ultra-low DMG of 0.007 dB and minimum modal gain (MMG) of about 24.890 dB are obtained at the wavelength of 1550 nm.