Optical Single-Sideband Transmitters

Optical single-sideband (SSB) transmission technique fills the gap between intensity-modulation/direct-detection (IM/DD) and digital coherent transmission technologies. It provides a cost-effective solution to overcome the transmission distance limitation induced by fiber chromatic dispersion in IM/DD system at the expense of increased complexity of the transmitter (Tx) structure and receiver-side signal processing. This makes optical SSB system become a promising candidate for cost- and latency-sensitive datacenter interconnects. Previous research on optical SSB system mainly focused on improving the spectral efficiency and receiver sensitivity, whereas the increased complexity and cost of optical SSB Tx were overlooked. In this paper, we present a comprehensive review of the recent advances in the optical SSB Tx. First, we evaluate three conventional optical SSB Tx schemes based on optical filter, in-phase/quadrature modulator, and dual-drive Mach-Zehnder modulator. We then introduce the recently proposed optical SSB Tx schemes based on electro-absorption modulation lasers (EMLs), including the double-sided EML, two-segment EML, and the dually modulated EML. Compared with the conventional optical SSB Tx solutions, the EML-based schemes exhibit obvious friendliness to monolithic integration. Besides, we investigate the practical ways to add optical carrier with optical SSB signal and efficient implementation of the Hilbert transform, which are two practical issues in the optical SSB Tx. Finally, we explore the capability of monolithic integration of optical SSB Tx with state-of-the-art material platforms. Our comparison made among these schemes can provide a guideline for the selection of proper Tx scheme for specific optical SSB systems.