Most current Data Center Interconnects (DCI) use intensity modulation direct detection (IMDD) configurations due to their low complexity and cost. However, significant scaling challenges allow coherent solutions to become contenders in these short reach applications. We present an O-band coherent optical fiber transmission system based on Quantum Dot—Mode Locked Lasers (QD-MLLs) using two independent free-running comb lasers, one each for the carrier and the Local Oscillator (LO). Using a comb-to-comb configuration, we demonstrate a 10 km single mode fiber, O-band, coherent, heterodyne, 12.1 Tbps system operating at 0.47 Tbps/λ using 26 λs. We used fewer comb lines (26 λs), faster symbol rate (56 GBaud) and higher constellation cardinality (32 QAM) relative to the highest capacity C-band systems reported to date. Through design, analysis, and experimentation, we quantify the optimum comb line spacing for this use case. We compare potential configurations for increasing data center interconnect capacities whilst reducing power consumption, complexity, and cost.

A new frequency-domain wave-propagation model that includes a position- and time-dependent carrier lifetime and the effect of amplified spontaneous emission is introduced and used to accurately simulate recovery time experiments in 0.5- and 1.0-mm long semiconductor optical amplifiers. It is compared to a constant lifetime model at different saturation levels, showing better performance and consistency. The role of the amplified spontaneous emission in saturated amplifiers is also discussed.

With the exponential growth of internet traffic, driven by the increasing number of connected devices and data-intensive applications, there is an urgent need to address the surging demand for higher capacity in datacenter communications. This paper proposes using O-band single-carrier coherent transmission to achieve 1.6 Tbps for intra-datacenter reach (2-10 km), leveraging the advancements in next-generation DACs and the TFLN platform. To support our proposal, we assess experimentally the gain of employing 256 GSa/s interleaved DACs compared to the current state-of-the-art 128 GSa/s DACs. Additionally, we explore the feasibility of utilizing cost-effective DFB lasers in these short-reach systems. Using the 128 GSa/s DAC and DFB lasers, we transmit 120 Gbaud DP-64QAM over 10 km of SSMF under the 20% overhead SD-FEC threshold, featuring a net rate of 1.2 Tbps. Switching to 256 GSa/s DAC, we achieve net 1.6 Tbps transmission over 10 km with 167 Gbaud DP-64QAM below the 25% SD-FEC BER threshold. We observe that the power penalty of using DFB lasers compared to ECLs is less than 1 dB. Furthermore, this study includes a comprehensive analysis of the power consumption envelope for various candidate configurations targeting 1.6 Tbps operation. The comparison reveals the competitiveness of the O-band single-carrier coherent solution, attributed to its simpler architecture and the inherent features of the TFLN platform. The analysis highlights the potential of the proposed solution as a power-efficient and high-performance option for meeting the demanding requirements of 1.6 Tbps Ethernet.

With the unprecedented growth of internet traffic, driven mainly by the recent surge of artificial intelligence and data-intensive applications, the need to address the demand for higher capacity datacenter interconnects is pressing. This invited article presents a study and experimental demonstration for achieving the future generation of 1.6 Tbps Ethernet standards. More specifically, this work presents an empirical demonstration of 1.6 Tbps at 2 and 10 km using the 4$\lambda$ LAN-WDM grid with cost and power effective uncooled DFB lasers, sub-1V driving voltages, low half-wave voltage and high-bandwidth TFLN modulators and quantum-dot SOAs. At 2 km, 1.33 Tbps was achieved using 210 GBaud PAM4 under the 25% OH SD-FEC threshold, 1.6 Tbps using 200 GBaud PAM6 under the 25% OH SD-FEC threshold, and 160 GBaud PAM8 under the 20% OH SD-FEC threshold. At 10 km, due to larger CD, 1.6 Tbps was achieved with asymmetrical channel loading where the edge-most channel used 130 GBaud PAM8 while the remaining three channels used 170 GBaud PAM8 where combined provide an aggregate net throughput of 1.6 Tbps under the 20% OH SD-FEC threshold. These results are followed by an analysis of the impacts of CD-induced power fading on data transmission at 2, 10, 20, and 40 km for channel rates of 100, 200, and 400 Gbps. This analysis reveals that channel rates of 400 Gbps are implementable at distances up to 10 km using WDM grids wide enough to accomodate for the use of uncooled lasers, but are practically unfeasible at distances larger than 10 km. Instead, for these longer reaches, channel rates of 100 Gbps are favorable due to lower accumulated CD.