Fiber Coupling Loss Mitigation of Wavelength Division Multiplexed 20 Gb/s QPSK Signal with 3-Mode Fiber

We evaluated fiber coupling loss mitigation by coupling light into a 3-mode fiber instead of a single mode fiber with 5 wavelength division multiplexed 4 Gb/s QPSK signals. The results of a free space optical communication experiment showed that even with a wavelength division multiplexed signal, this mitigation leads to 1.5 times greater tolerance to angular error of the light entering the receiver.