Brian Teipen

Adaptive Data Rates for Flexible Transceivers in Optical Networks

Efforts towards commercializing higher-speed optical transmission have demonstrated the need for advanced modulation formats, several of which require similar transceiver hardware architecture. Adaptive transceivers can be built to have a number of possible operational configurations selected by software. Such software-defined transceiver configurations can create specific modulation formats to support sets of data rates, corresponding tolerances to system impairments, and sets of electronic digital signal processing schemes chosen to best function in a given network environment. In this paper, we discuss possibilities and advantages of reconfigurable, bit-rate flexible transceivers, and their potential applications in future optical networks.

Flexible bandwidth and bit-rate programmability in future optical networks

Recent progress in network equipment allows trade-offs to be made between the optical bandwidth, distance-reach, and bit-rate for given optical data channels. We discuss methods to increase the utilization of network resources and thereby to lower the networks cost-per-bit of transport.

Adaptive optical transmission for dynamic optical networks

Efforts towards commercializing higher-speed optical transmission have demonstrated the need for advanced modulation formats, several of which require similar transceiver hardware architecture. Adaptive transceivers can be built which have different operational configurations controlled by software. These software-defined transceiver configurations support a set of specific modulation / demodulation formats, with respective data rates and tolerances to system impairments, as well as sets of electronic digital signal processing schemes, chosen to best function in a given network environment. In this paper, we discuss possibilities and advantages of reconfigurable and dynamically-adaptive transceivers, and their potential applications in future optical networks.

DPSK-3ASK transmission optimization by adapting modulation levels

For metro and regional 100-Gbps transmission, a transparent channel reach of 500-600 km is required and a 100-GHz channel grid is typically used. For these applications, a cost effective modulation format is introduced which can make use of electronic components designed for the already established 40-Gbps market, bypassing the requirements for novel electronic developments and therefore reducing the component cost. With this DPSK-3ASK modulation format, five information bits are transmitted in two consecutive symbols, leading to a symbol rate of 45 Gbaud, including overhead for framing and FEC. To minimize hardware requirements and to create a cost-effective solution, a single Mach-Zehnder modulator can be used to create the optical DPSK-3ASK signal after combining the phase and amplitude modulation signals into a 6-level modulator drive voltage. In this paper, it is demonstrated by numerical simulations that these voltage levels can be modified to adapt to varying signal distortions and thereby yield improved transmission performance. It is shown that by dynamically modifying the modulation levels based on the channel performance, dynamic signal impairments such as the non-linear effects from varying power levels, changes in chromatic dispersion, or varying PMD levels can be mitigated. Error-free performance (with FEC) can be obtained with 24 dB OSNR and 7ps DGD for a 112-Gbps (45-Gbaud) optical signal.

Investigation of PAM-4 for extending reach in data center interconnect applications

Optical four-level pulse amplitude modulation (PAM-4) is being widely studied for various short-reach optical interfaces, motivated by the need to keep cost structure low, and to increase link capacity despite various constraints in component bandwidth. When considering PAM-4 in applications with reach significantly greater than 10 km, such as in extended data center interconnects which require optical amplification, impairments such as chromatic dispersion, optical filtering, and ASE must be controlled. We investigate and report on requirements of PAM-4 for extended-reach, data center interconnect links.

Field trial of a 1250-km private optical network based on a single-fiber, shared-amplifier WDM system

We report the first field trial of an ultra-longhaul WDM transmission system with a single-fiber, shared-amplifier architecture over a fourteen-span, 1250-km optical link with mixed fiber types for remote data replication in storage area networks.

107Gb/s DPSK-3ASK optical transmission over SSMF

We report on the transmission of a 107Gb/s DPSK-3ASK optical channel over 335km, fiber (SSMF). DPSK-3ASK is targeted to meet the requirements of a metro network.

Balancing the benefits inherent in reconfigurable coherent optical transceivers

Starting with transmission performance from commercially available 100+ Gb/s DP-QPSK transceivers, we calculate relative distance reach penalties and corresponding spectral efficiency improvements made possible with DSP-based pulse shaping and quasi-Nyquist subcarrier spacing. Modulation formats for nominal rate 400 Gb/s and 1.6 Tb/s superchannels, for different symbol rates, subcarrier spacing, and guardbands are considered in the context of a flexible grid. A 12.5 GHz frequency slot granularity results in discretization of operating parameters. Cases are highlighted in which distance reach penalties are incurred without the desired improvements in spectral efficiency; avoidance of such cases is expected to increase link reliability.

Wavelength-agnostic WDM-PON system

Next-generation WDM-PON solutions for metro and access systems will take advantage of remotely controlled wavelength-tunable ONUs to keep system costs as low as possible. For such a purpose, each ONU signal can be labeled by a pilot tone modulated onto the optical data stream. We report on the standardization status of this low-cost system in the new ITU-T G.metro draft recommendation, in the context of autonomous tuning. We also discuss some low-effort implementations of the pilot-tone labels and investigate the impact of these labels on the transmission channels.

Forward error correction trade-offs in reduced-latency optical fiber transmission systems

100G DP-QPSK transmission can use programmable SD-FEC to trade-off latency against coding gain. Albeit inferior to 10G ultra-low latency implementations, such a solution can approach state-of-the art 10G G.709 FEC transmission in latency and performance while offering a 10x capacity increase.