Nokia of America Corporation

Ronen Dar

Cristian B Czegledi

Peter Johannes Winzer

Szilard Zsigmond

An amplified optical link having a fault-protection capability that is based, at least in part, on the ability to selectively and independently power up and down different groups of optical amplifiers within the link. In an example embodiment, the optical link is implemented using an optical fiber cable having an electrical power line and arrays of optical amplifiers connected between successive optical fiber segments to form a plurality of disjoint groups of parallel optical paths between the ends of the optical fiber cable. The electrical power line is operable to selectively power, as a group, the optical amplifiers of at least some of the disjoint groups. In various embodiments, different optical paths can be implemented using different respective strands of a single-core optical fiber, different respective cores of a multi-core optical fiber, and/or different respective sets of spatial modes of a multimode optical fiber.

Amplified optical link having a fault-protection capability

An optical transport system configured to compensate nonlinear signal distortions using a backward-propagation algorithm in which some effects of polarization mode dispersion on the nonlinear signal distortions are accounted for by employing two or more different approximations of said effects within the bandwidth of the optical communication signal. In an example embodiment, the corresponding digital signal processor (DSP) is configured to switch between different approximations based on a comparison, with a fixed threshold value, of a difference between frequencies of various optical waves contributing to the nonlinear signal distortions, e.g., through four-wave-mixing processes. In different embodiments, the backward-propagation algorithm can be executed by the transmitter's DSP or the receiver's DSP.

Backward propagation with compensation of some nonlinear effects of polarization mode dispersion

A WDM receiver configured to apply electronic equalization processing to both dispersion-compensated and dispersion-distorted versions of the received communication signal. In an example embodiment, the receiver's DSP first generates an equalized dispersion-compensated signal corresponding to the communication signal. The DSP then performs electronic dispersion-application processing on the equalized dispersion-compensated signal to generate a dispersion-distorted version thereof. The DSP then applies decision-aided electronic equalization processing to the dispersion-distorted version of the signal, subjects the resulting equalized signal to another round of dispersion-compensation processing, and recovers the data encoded in the communication signal using the resulting dispersion-compensated signal. This chain of signal processing tends to be effective in reducing nonlinear distortions of the intra-channel type and also some effects of nonlinear inter-channel interference, which advantageously enables the WDM receiver to support a lower BER and/or a higher data-transport capacity than those achievable with conventional WDM receivers.

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Ronen Dar