Multimode Erbium-Doped Fiber Amplifier Based on Double-Clad GeO2-Doped Photonic Crystal Fiber Supporting 38 Orbital Angular Momentum Modes

We propose a novel fiber design of multimode EDFA(MMEDFA) for the amplification of 38 orbital angular momentum(OAM) modes (l=1 to 10). The MMEDFA is based on double-cladGeO2-doped photonic crystal fiber (PCF) with only two layers ofair holes. The combined effect of the doped annulus core and the airholes in the fiber cladding results in the confinement loss lower than4.34x10(-10)dB/m and ensures that the minimum separationbetween adjacent vector eigenmodes is greater than1.8x10(-4).The mode effective area of all the supported eigenmodes is morethan230 mu m(2),whichresultsinlowvaluesofnon-linearityacrosstheC bandwidth. The gain of 38 signal OAM modes is more than 26 dB,and the differential modal gain (DMG) is less than 0.13 dB acrossthe C-band. The noise figure is below 4.14 dB for all the supportedsignal OAM modes. The proposed MMEDFA will be useful in modedivision multiplexing systems, providing relay amplification of allattenuated signal OAM modes.