Roadmap of optical communications

© 2016 IOP Publishing Ltd. Lightwave communications is a necessity for the information age. Optical links provide enormous bandwidth, and the optical fiber is the only medium that can meet the modern society's needs for transporting massive amounts of data over long distances. Applications range from global high-capacity networks, which constitute the backbone of the internet, to the massively parallel interconnects that provide data connectivity inside datacenters and supercomputers. Optical communications is a diverse and rapidly changing field, where experts in photonics, communications, electronics, and signal processing work side by side to meet the ever-increasing demands for higher capacity, lower cost, and lower energy consumption, while adapting the system design to novel services and technologies. Due to the interdisciplinary nature of this rich research field, Journal of Optics has invited 16 researchers, each a world-leading expert in their respective subfields, to contribute a section to this invited review article, summarizing their views on state-of-the-art and future developments in optical communications

Space Division Multiplexing in Optical Fibres

Optical communications technology has made enormous and steady progress for several decades, providing the key resource in our increasingly information-driven society and economy. Much of this progress has been in finding innovative ways to increase the data carrying capacity of a single optical fibre. In this search, researchers have explored (and close to maximally exploited) every available degree of freedom, and even commercial systems now utilize multiplexing in time, wavelength, polarization, and phase to speed more information through the fibre infrastructure. Conspicuously, one potentially enormous source of improvement has however been left untapped in these systems: fibres can easily support hundreds of spatial modes, but today's commercial systems (single-mode or multi-mode) make no attempt to use these as parallel channels for independent signals.Comment: to appear in Nature Photonic

Experimental study of XPM in 10-Gb/s NRZ precompensated transmission systems

\u3cp\u3eWe experimentally assess the nonlinear tolerance of 10-Gb/s NRZ in a precompensated dispersion map. It is observed that even for relatively wide 100-GHz channel-spacing, XPM further reduces the nonlinear tolerance in contrast to periodically-compensated maps.\u3c/p\u3

Long-haul DWDM transmission systems employing optical phase conjugation

In this paper, we review the recent progress in transmission experiments by employing optical phase conjugation (OPC) for the compensation of chromatic dispersion and nonlinear impairments. OPC is realized with difference frequency generation (DFG) in a periodically poled lithium-niobate (PPLN) waveguide, for transparent wavelength-division multiplexed (WDM) operation with high conversion efficiency. We discuss extensively the principle behind optical phase conjugation and the realization of a polarization independent OPC subsystem. Using OPC for chromatic dispersion compensation WDM 40-Gb/s long-haul transmission is described. As well, transmission employing both mixed data rates and mixed modulation formats is discussed. No significant nonlinear impairments are observed from the nonperiodic dispersion map used in these experiments. The compensation of intrachannel nonlinear impairments by OPC is described for WDM carrier-suppressed return-to-zero (CSRZ) transmission. In this experiment, a 50% increase in transmission reach is obtained by adding an OPC unit to a transmission line using dispersion compensating fiber (DCF) for dispersion compensation. Furthermore, the compensation of impairments due to nonlinear phase noise is reviewed. An in-depth analysis is conducted on what performance improvement is to be expected for various OPC configurations and a proof-of-principle experiment is described showing over 4-dB improvement in Q-factor due to compensation of nonlinear impairments resulting from nonlinear phase noise. Finally, an ultralong-haul WDM transmission of 22×20-Gb/s return-to-zero differential quadrature phase-shift keying (RZ-DQPSK) is discussed showing that OPC can compensate for chromatic dispersion, as well as self-phase modulation (SPM) induced nonlinear impairments, such as nonlinear phase noise. Compared to a conventional transmission link using DCF for dispersion compensation, a 44% increase in transmission reach is obtained when OPC is employed. In this experiment, we show the feasibi

Interchannel nonlinear transmission penalties in polarization-multiplexed 2x10 Gbit/s DPSK

We discuss the performance of a multichannel 2 3 10 Gbit/s polarization-multiplexed differential phaseshift keying transmission system. Through simulations and transmission experiments we find that, despite the constant power envelope of non-return-to-zero phase-shift keying modulation formats, polarization multiplexing strongly reduces the nonlinear tolerance and transmission performance at a 2 3 10 Gbit/s line rate with multichannel transmission. This results in a 10 dB power penalty when comparing single- and nine-channel transmission. Additionally, multichannel impairments in differential phase-shift keying and on–off keying are compared for 2 3 10 Gbit/s polarization-multiplexed transmission. © 2005 Optical Society of Americ

Wavelength conversion of a 40-Gb/s NRZ signal across the entire C-band by an asymmetric Sagnac loop

A compact integrated all-optical wavelength converter based on an asymmetric Sagnac loop is demonstrated. We show that a 40-Gb/s nonreturn-to-zero data signal can be converted over the entire C-band employing an asymmetric Sagnac loop. Compared to the back-to-back configuration, a receiver sensitivity power penalty of less then 2.1 dB is measured for both up- and down-conversion

Applications of optical phase conjugation in robust optical transmission systems

\u3cp\u3eIn this paper, WDM transmission experiments are discussed showing simultaneous compensation of nonlinear effects and chromatic dispersion through optical phase conjugation (OPC). The performance of OPC and DCF for chromatic dispersion compensation are compared in a wavelength division multiplexed (WDM) transmission link with 50-GHz spaced 42.8-Gb/s RZ-DQPSK modulated channels. The feasible transmission distance for a Q-factor ∼10 dB is limited to approximately 5,000 km and 3,000 km for the OPC and the DCF based configuration, respectively. When the Q-factor as a function of the transmission distance is observed, at shorter distances, the Q-factor of the OPC based configuration is about 1.5 dB higher than that of the DCF based transmission system. Up to 2,500-km transmission a linear decrease in Q is observed for both configurations. After 2,500-km transmission, the Q-factor of the DCF based configuration deviates from the linear decrease whereas the OPC based performance is virtually unaffected.\u3c/p\u3