Bi-Directional Self-Homodyne Transmission With MIMO-Free DSP for Next-Generation Data Center Interconnects

We propose and demonstrate bi-directional (BiDi) self-homodyne coherent detection (SHCD) system experimentally, in which the multiple input multiple output free (MIMO-free) digital signal processing (DSP) is achieved with the help of BiDi-operated adaptive polarization controller (APC). Since the polarization wandering of the local oscillator (LO) is relevant to that of the counter-propagating signal within the same fiber, the APC can realize the polarization tracking and compensation for LO and the counter-propagating signal simultaneously. The power-consuming 2x2 MIMO DSP, can be eliminated in our proposed BiDi SHCD system. The frequency offset compensation (FOC), carrier phase recovery (CPR) are also omitted thanks to the SHCD. Besides, the dedicated chromatic dispersion compensation (CDC) is no longer needed due to short-reach transmission of data center interconnect (DCI). We validate in experiment the proposed system using 23GBaud DP-32QAM signal delivering 230Gb/s over 2 km of single mode fibers (SMFs) with the laser-linewidth tolerance of 1MHz. The parameters of polarization tracking algorithm are optimized to attain the polarization rotation tolerance up to 850 rad/s under the FEC threshold of 2x10
⁻²
. The proposed BiDi SHCD system achieves the coherent-lite DSP without MIMO, FOC, CPR and dedicated CDC algorithm in dynamic state of polarization (SOP) rotation while maintaining the full spectral efficiency (SE) of traditional coherent system.