Analytical Investigation on Self-Homodyne Coherent System Based on Few-Mode Fiber

We present an analytical investigation on the amplified spontaneous emission-limited self-homodyne coherent system based on a few-mode fiber. We test the accuracy of our model in the context of 112 Gb/s polarization-multiplexed quadrature phase-shift keying (QPSK) transmission through this system. We find that the application of dc offset elimination is necessary to reduce distortion of QPSK constellation. Meanwhile, a closed-form analytical bit error ratio (BER) formula is verified by numerical simulations with deviation at BER=10^-3, whereas the predicted optimum power ratio between data signal and pilot-tone signal agrees well with the simulation result. In addition, the adaptive equalization using modified constant modulus algorithm is shown effectively for the proposed system. The tolerance of residual time delay is ±18 ns after carrier phase alignment using optical delay line, given 0.5 dB optical signal-to-noise ratio penalty at BER=10^-3.