The gain equalization of six-mode signals by few-mode bismuth-doped fiber amplifier operating in O-band

Abstract

In this paper, an O-band few-mode fiber amplifier is numerically simulated based on our proposed few-mode bismuth-doped fiber. The different pump modes and powers, signal powers, doping concentrations, and different combinations of mode pumps are adopted to investigate the gain, mode gain difference (DMG), and noise figure under four-mode signal groups including LP01, LP11, LP21, and LP02. The results show that (1) the single-mode pump can achieve gain equalization of two-mode signal groups at the pump wavelength of 808 nm and the signal wavelength of 1300 nm. The minimum DMG between the two-mode signal groups is only 0.2 dB with the LP11 or LP21 pump is used alone at the pump power of 5 W; (2) The combination of different modes of pump can achieve gain equalization of four-mode signal groups under the same pump and signal wavelength. With the combination of LP21 and LP02 mode pumps at 5 W power, the average gain of the four-mode signal group exceeded 25 dB, and the maximum DMG is 2.9 dB, which is 56% higher and 85% lower than if only the LP21 pump is used. The simulations suggest the great potential of our proposed fiber as a material for an O-band few-mode fiber amplifier.