A photonic crystal fiber amplifier for orbital angular momentum Raman amplification.

To resolve the issue of high-quality propagation and amplification of orbital angular momentum modes derived from the Raman effect and doped materials, a photonic crystal fiber amplifier, which can amplify orbital angular momentum modes, is proposed in this paper. Through modifying the structure and doping material concentration of the amplifier, the performance of the amplifier is optimized and then systematically investigated through finite element method simulations using COMSOL Multiphysics® (multiphysics simulation software) version 6.2. The results reveal that the amplifier can realize the steady propagation of 38 orbital angular momentum (OAM) modes, and the amplifier exhibits excellent amplification performance, characterized by high mode gain and low threshold power. The threshold power of all modes does not exceed 250 mW, which is conducive to signal amplification. As the pump light has an incident power of 300 mW, a wavelength of 1450 nm, and a wavelength of the OAM signal of 1550 nm, the maximum mode gain of 160.87 dB can be obtained. Compared with the existing orbital angular momentum amplifier, the signal gain has been greatly improved. The proposed amplifier has the advantages of high gain, low threshold power, and a large number of amplified modes, which has significant applications in achieving long-distance stable propagation of OAM and enhancing the capacity of optical fiber communication systems.