Collective compensation of an inter-chip intensity discrepancy for a 4ch QPSK FE-SOCDM system with Si-based ODFT and electrical DFT

An intensity-sloped optical code with an optical chip-pulse stream generated by Si-based ODFT suffers from crosstalk and signal-to-noise (SNR) degradation. To mitigate these problems related to code-orthogonality reduction, we propose a simple intensity-discrepancy-compensation scheme that involves adjusting the chip-level intensity in the digital-domain. We numerically show a 0.1 dB SNR improvement for 40 Gb/s quadrature phase-shift keying (QPSK) Fourier-encoded synchronized optical code division multiplexing (FE-SOCDM) signal when multiplexing 1 dB/chip intensity-sloped optical codes. A proof-of-principle experiment achieves a 0.3 dB received power improvement using intensity-discrepancy compensation for two optical code multiplexing signals with 1.5 dB/chip.