The different segments of optical transport networks—including metro, regional, and long-haul—will have to scale to accommodate growing capacity requirements. In metro networks, lower capacity (compared to the other two segments) but more stringent power consumption and interoperability requirements will likely favor the adoption of pluggable coherent interfaces, whereas in long-haul, the best-in-class spectral efficiency of embedded proprietary coherent interfaces is paramount. However, it is less clear which will be the interface type of choice in regional transport networks. This paper compares different strategies to increase the capacity of regional transport networks, which not only exploit the usage of pluggable or embedded interfaces but also enhanced line system solutions, comprising the SuperC-band and hybrid Raman/erbium-doped fiber amplification. Simulation results obtained in two reference regional-sized networks highlight that the utilization of embedded coherent interfaces enables a considerably higher traffic load to be supported over the existing fiber infrastructure, even when the usage of pluggable interfaces is complemented with exploiting the SuperC-band and hybrid amplification. Moreover, for the same transported traffic load, the simulation results also show that embedded interfaces can reduce by up to half the number of line interfaces required, when compared to pluggable interfaces.

We report on the development of a two-channel digital coherent optics (DCO) module, based on a monolithic InP photonic integrated circuit (PIC) transceiver and SiGe application-specific integrated circuit (ASIC), paired with a real-time 7 nm digital signal processing (DSP) ASIC. The high-performance coherent optical engine, which utilizes digital Nyquist subcarriers and probabilistic constellation shaping (PCS) techniques, enables long-haul and ultra-long-haul transmission distances over mixed fiber and amplifier types. This work discusses the performance of a DCO unit operating at multiple data rates over three practical real-world-like network distances. 800 Gb/s data transmission over a 1,000 km standard single mode fiber link was achieved using a 96 GBd, PCS-64QAM modulation format. Results of extended reaches of over 2,400 km and 5,000 km are also presented with data rates of 600 Gb/s and 400 Gb/s, respectively.

This paper provides insight on the role of next-generation coherent interfaces and use of an extended C-band to cost-effectively scale regional transport networks.

Optical communications are the key enabler for the ever-increasing traffic growth as they allow multiplexing a number of carriers onto a single optical fiber. However, network deployments are becoming more challenging due to the large bandwidth increments. Indeed, the fiber planning process is a slow, costly, and strategic activity for network operators, who must decide where to rent or deploy additional capacity. Depending on the long-term view, the network operator will define a fiber plan which may require high capital expenditure (CAPEX) investments to deploy additional multiple fiber pairs between central offices. During the last few years, C&L-band technologies have evolved to a point where they are now strong candidates to extend the fiber lifetime of these high capacity links. This article aims to present the evolution of C&L-band systems from a network design perspective, covering transmission and optical amplifier capabilities, demand optimization phase, showing a record demonstration of 56.4 Tb/s C&L-band 800 km transmission using commercial C&L-band system technology.

The design of application-specific integrated circuits (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. First, we describe the key-building blocks of modern high-speed DSP-based transponders working at up to 800G per wave. Second, 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 x 800G).

We present multi-channel monolithically integrated InP based photonic integrated circuits emitting in both the C and L bands with 200 Gbps transmission per wavelength, enabling long haul links with up to 57.6 Tbps capacity.

We analyze the impact of cloud, mobile, and NFV architectures on transport networks using advanced traffic models and emerging optical technologies. We show robustness of converged optical/digital switching designs with carrier speeds up to 600Gb/s.

We show real-time measurement of error-free superchannel transmission over more than 10,500 km of large-area fiber at a spectral efficiency of 4.66 b/s/Hz, utilizing subcarrier based signal processing optimized at 5.4 GBd.

We study the effects of higher modulation formats on the design of optical network architectures using Flexible Grid and Sliceable Bandwidth Variable Transponders. We show architectures with digital switching getting more benefit from higher modulation.

We discuss pump requirements for co-propagating distributed Raman amplification. We demonstrate a depolarized pump source with sufficiently low and stable degree of polarization. We demonstrated system benefits with no noticeable problems from pump-mediated cross-talk.