Blind transmitter IQ imbalance compensation in M-QaM optical coherent systems

We investigate transmitter IQ imbalance compensation based on the blind adaptive source separation (BASS) method in a dual-polarization M-QAM optical coherent system. The robustness of the BASS method against the residual carrier frequency offset (CFO) is numerically investigated and compared to that of the Gram-Schmidt or-thogonalization procedure (GSOP). We further validate experimentally the proposed method with 10 Gbaud optical 4-QaM and 16-QAM signals at 30° and 10° phase imbalance, respectively, with simulated impairments. More specifically, in the presence of 5 χ 10
⁻⁶
residual CFO (normalized to the sample rate), the optical signal-to-noise ratio penalty reduction of the BASS method compared to the GSOP method is 1 dB for 4-QAM at a bit error ratio (BER) of 2 χ 10
⁻³
and 2 dB for 16-QAM at a BER of 10
⁻³
. In contrast to the GSOP, which requires an independent block, the BASS method can be integrated into an equalizer, simplifying the operation and allowing parallel implementation.