800G DSP ASIC Design Using Probabilistic Shaping and Digital Sub-Carrier Multiplexing

Abstract

The design of application-specific integrated circuit (ASIC) is at the core of modern ultra-high-speed transponders employing advanced digital signal processing (DSP) algorithms. This manuscript discusses the motivations for jointly utilizing transmission techniques such as probabilistic shaping and digital sub-carrier multiplexing in digital coherent optical transmissions systems. We firstly report the key-building blocks of high-speed modern DSP-based transponders working up to 800G per wave. Secondly, we show the benefits of these transmission methods in terms of system level performance. Finally, we report, to the best of our knowledge, the first long-haul experimental transmission -e.g., over 1000 km -with a real-time 7 nm DSP ASIC and digital coherent optics (DCO) capable of data rates up to 1.6 Tb/s using two waves (2×800G).

Chromatic Dispersion-Aware Carrier-Phase Estimation for Digital Subcarrier Multiplexing Systems

“…We present the results of subcarrier-independent pilot-based CPE and DRS algorithms for 4, 8, and 32 SCs. In all cases, the DRS algorithm is shown to clearly outperform the best subcarrierindependent pilot-based approach, while enabling an ever-increasing performance with higher SC count, thus overcoming the well-known degradation of MSC performance with lower SC symbol rates [1] . It is worth noting that the gain provided by the DRS algorithm is further evidenced for large combined linewidths.…”

“…Digital subcarrier multiplexing systems have been gaining both academic and commercial interest lately due to their associated advantages [1]- [6] , namely in terms of inherent DSP parallelism, enhanced bit-rate granularity [2], [3] and higher tolerance against Chromatic Dispersion (CD) [4] , Nonlinear Interference Noise (NLIN) [5], [6] and Equalization-Enhanced Phase Noise (EEPN) [1] . However, they also still present an important disadvantage from the Carrier Phase Estimation (CPE) point of view, due to the increased symbol periods [1] . In order to try and circumvent this limitation, several joint-subcarrier CPE schemes have been proposed [7]- [9] , but these solutions are not specifically aimed at maintaining the increased tolerance to CD that is brought by MSC systems.…”

Challenges and Trade-offs in Real-Time Implementation of DSP for Coherent Transmission

“…It is challenging to implement ADCs with high sampling rates. While digital subcarrier multiplexing offers one path to limiting symbol rate at the system level [3,13], choice of oversampling is a trade-off available during receiver implementation. An oversampling of 2 samples per symbol (SPS) has been common, since this choice relaxes ADC requirements and enables powerful equalization schemes [7].…”

Simulative assessment of non-linear interference generation within disaggregated optical line systems

“…The current and future requirements from optical line system (OLS) operators, cloud service providers and end users are producing a progressive yearly increase in demand for higher transmission rates and larger optical network capacities and throughput [1]- [3] . Correspondingly, optical networks are shifting to a format that enables a greater degree of flexibility with respect to wavelength assignment, transmission standards and symbol rates, representing a shift towards a disaggregated structure [4]- [6] . A fully disaggregated network approach requires all OLS components to be considered independently [7] , as they may be controlled by different network providers and operators.…”