We review margins used in optical networks and review a formerly proposed margin taxonomy. For each category of margins, we review techniques that the network designer can use in order to increase the capacity of optical networks, extend their life, and decrease deployment cost (CAPEX) or total cost of ownership over their life duration. Green field (new network deployments) and brown field techniques (used after initial network deployment) are discussed. The technology needed to leverage the margins and achieve the aforementioned gains are also reviewed, along with the associated challenges.

Design of Low-Margin Optical Networks

We review the recent technology advancements related to the transmission of 400Gb/s, wavelength-division-multiplexed channels for optical networks based on the standard 50 GHz grid We discuss the enabling modulation, coding, and line system technologies, as well as the existing challenges Specifically, these technologies include time-domain hybrid 32-64 quadrature amplitude modulation, nearly ideal digital Nyquist pulse shaping, improved channel bandwidth management methods such as end-to-end carrier frequency control and distributed compensation of filtering effects arising from reconfigurable optical add/drop multiplexers, distributed Raman amplification, and powerful forward error correction We demonstrate 400G transmission on the standard 50 GHz grid over meaningful transmission reach for regional and metropolitan applications However, further studies are needed to fully understand the potential for meeting the requirements of long-haul transmission applications

400G WDM Transmission on the 50 GHz Grid for Future Optical Networks

In this paper, we present the design and analysis of an adaptive cost-effective discrete multitone transponder (DMT) using direct detection (DD) suitable for data center interconnections. Levin Campello margin adaptive (LC-MA) algorithm is applied to the transponder digital signal processing modules to enhance fiber chromatic dispersion (CD) resilience, while achieving high-data rate transmission. The bit error rate (BER) performance and the rate/distance adaptive capabilities of the proposed transponder have been numerically analyzed and compared to bandwidth variable uniform loading, taking into account the transmission impairments at the varying of the fiber length. Specifically, the performance of the designed transponder has been assessed from $20$
 to $112$
 Gb/s, extending the achievable reach at $50$
 Gb/s beyond $80$
 km of standard single mode fiber (SSMF). The numerical simulations have been compared with experimental results, evidencing good agreement in presence of transmission impairments.

DMT Modulation With Adaptive Loading for High Bit Rate Transmission Over Directly Detected Optical Channels

We demonstrate high speed optical transmission systems using digital coherent detection at all-electronically multiplexed symbol rates of 80 and 107 Gbaud. At 107 Gbaud, we demonstrate a single-carrier polarization division multiplexed quadrature phase shift keyed (PDM-QPSK) line rate of 428 Gb/s. At 80 Gbaud, we achieve a single-carrier line rate of 640 Gb/s using PDM 16-ary quadrature amplitude modulation (16-QAM). Using two optical subcarriers, we demonstrate a 1-Tb/s optical interface and conduct long-haul wavelength-division multiplexed (WDM) transmission on a 200-GHz grid over 3200 km of ultra-large effective area fiber.

High Symbol Rate Coherent Optical Transmission Systems: 80 and 107 Gbaud

In this paper we describe the boundary conditions for upgrading existing 10 G optical transport networks with 40 G and 100 G channels and the operational issues in multi-rate optical networks.

Multi-rate (100G/40G/10G) Transport Over Deployed Optical Networks

We demonstrate a 120 Gb/s coherent polarization-multiplexed quadrature-phase-shift-keyed transceiver with soft-decision forward-error-correction (SD-FEC) coding based on Turbo Product Code. This industry-first transceiver module utilizes a 40 nm complementary metal-oxide semiconductor (CMOS) application-specific integrated circuit with integrated analog-to-digital conversion, digital signal processing and SD-FEC, and is packaged according to a multi-source agreement from the Optical Internetworking Forum. Through several long-haul and ultra-long-haul system experiments (over 1000 km to 3760 km), we validate the robustness of the transceiver and demonstrate its high tolerance to various system impairments, including fiber nonlinearity, chromatic dispersion up to 60,000 ps/nm, polarization mode dispersion, polarization-dependent loss, polarization transients and multiple-path interference.

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A robust real-time 100G transceiver With soft-decision forward error correction [Invited]

This paper presents the results of three practical experiments proving the viability of 40 Gbit/s phase-shaped binary transmission (PSBT) channel upgrade to existing 10G systems supporting 50 GHz channel spacing: (a) lab experiments with a fully loaded 1000 km 80-channel 10 Gbit/s system upgraded with two 40 Gbit/s PSBT channels, (b) an 850 km field trial of 40 Gbit/s PSBT channel upgrade to an installed 10 Gbit/s system and installed fiber, (c) an extension of the 850 km field trial to 1700 km via optical loop back. The 10 Gbit/s system was left as originally provisioned and all link control loops were active during the trials. Error free performance after FEC was achieved for all three experimental configurations, proving flexible and seamless 40 Gbit/s PSBT channel upgrade to existing 10 Gbit/s systems is possible and practical.

Field trial of a 40 Gbit/s PSBT channel upgrade to an installed 1700 km 10 Gbit/s system

We report error-free, 47×80km transmission of a real-time, 120Gbps, coherent PM-QPSK MSA transceiver with soft-decision forward-error-correction. Two cascaded commercial systems included 40G neighbors and ten ROADMs. The transceiver compensated 60,000ps/nm and had 2.5dB remaining margin.

3760km, 100G SSMF transmission over commercial terrestrial DWDM ROADM systems using SD-FEC

We demonstrated a 400Gb/s Ethernet end-to-end circuit, inclusive of 400GbE client card with CPF8 interface and dual-carrier 16QAM line-side, on a production 100G core network segment between New York City and Washington DC. During the field trial, we demonstrated the feasibility of SDN-enabled creation, deletion, and re-routing of the 400G service.

C. Skolnick

Papers

A robust real-time 100G transceiver With soft-decision forward error correction [Invited]

Field trial of a 40 Gbit/s PSBT channel upgrade to an installed 1700 km 10 Gbit/s system

3760km, 100G SSMF transmission over commercial terrestrial DWDM ROADM systems using SD-FEC

SDN-controlled 400GbE end-to-end service using a CFP8 client over a deployed, commercial flexible ROADM system