Synthesis of SSB Nyquist 16QAM From Twin-SSB QPSK Via Optical Subcarrier Processing-Based Data Aggregation and its Direct Detection With Hierarchical Blind Phase Search Algorithm

To synthesize a single-sideband (SSB) Nyquist high-order QAM, an optical subcarrier processing (OSP) based scheme is proposed and experimentally demonstrated. A Twin-SSB Nyquist in lower-order QAM is firstly generated using an electro-optic approach. OSP-based data aggregation is then deployed to coherently merge two sidebands in the twin-SSB to synthesize an SSB Nyquist QAM with an increased modulation level. The proposed scheme effectively relaxes the requirement for the digital-to-analog (DAC) resolution, thus reducing the power consumption and cost. Besides, the use of the coherent two-carrier pump in the data aggregation avoids the introduction of phase noise from the pump. It allows for the deployment of a low-cost laser as a pump laser source without sacrificing the performance, further reducing the overall implementation cost. Moreover, a hierarchical blind phase search algorithm is proposed to combat the possible distortions introduced in the data aggregation. A 12.5 Gbps SSB Nyquist 16QAM is experimentally synthesized from a 2 × 6.25 Gbps twin-SSB Nyquist QPSK with an error-free operation.