Polarization-dependent loss measurement on mode division multiplexing system for optimal transmission of high-speed dual-polarization signals

We propose a method for reducing the polarization-dependent loss (PDL) of mode division multiplexing (MDM) system with the help of a few-mode polarization controller (FMPC), in order to transport high-speed dual-polarization (DP) signals. The detailed PDL measurement is implemented by the commercial PSGA-101A polarization analyzer along with the external light source with the dual-polarization quadrature phase shift keying (DPQPSK) format, and the feasibility is verified by the back-to-back (B2B) MDM and MDM amplification systems. In the amplification system, the home-made few-mode erbium-doped fiber amplifier (FM-EDFA) is used for simultaneously amplifying four modes of LP01, LP11, LP21 and LP02, with the gain of more than 20 dB and the minimum differential modal gain (DMG) of 1.55 dB. By adjusting the FMPC to equalize the PDL, the entire MDM amplification system can provide optical power margin about 24 dB for DP-QPSK signals. In other words, the FMPC state can also be characterized by the PDL values.