With 100G technologies standardized, in the context of both Ethernet and the optical transport network (OTN), 100G router ports and 100G optical transport interfaces are commercially available. At the same time, heavily data-centric users are starting to ask for higher-rate interfaces. First speculations include 400G as well as 1T as the next possible Ethernet standards. In this article we discuss interface technology options for Ethernet and OTN beyond 100G in light of the current 100G standards, taking into account likely evolution paths of interface technologies over the next 10 years.

Beyond 100G Ethernet

We propose a novel “orthogonal” TDM transmission scheme using an optical Nyquist pulse that enables us to achieve an ultrahigh data rate and spectral efficiency simultaneously without any intersymbol interference (ISI). We analytically describe the principle of orthogonal TDM, and demonstrate a 160 Gbaud optical orthogonal TDM transmission using 40 GHz optical Nyquist pulses. Tolerance to GVD and the dispersion slope is significantly improved by virtue of the orthogonality, reduced bandwidth, and minimum ISI.

Ultrahigh-speed “orthogonal” TDM transmission with an optical Nyquist pulse train

Modulation formats for 100G and beyond

Coherent-detection (CoD) permits to fully exploit the four-dimensional (4D) signal space consisting of the in-phase and quadrature components of the two fiber polarizations. A well-known and successful format exploiting such 4D space is Polarization-multiplexed QPSK (PM-QPSK). Recently, new signal constellations specifically designed and optimized in 4D space have been proposed, among which polarization-switched QPSK (PS-QPSK), consisting of a 8-point constellation at the vertices of a 4D polychoron called hexadecachoron. We call it HEXA because of its geometrical features and to avoid acronym mix-up with PM-QPSK, as well as with other similar acronyms. In this paper we investigate the performance of HEXA in direct comparison with PM-QPSK, addressing non-linear propagation over realistic links made up of 20 spans of either standard single mode fiber (SSMF) or non-zero dispersion-shifted fiber (NZDSF). We show that HEXA not only confirms its theoretical sensitivity advantage over PM-QPSK in back-to-back, but also shows a greater resilience to non-linear effects, allowing for substantially increased span loss margins. As a consequence, HEXA appears as an interesting option for dual-format transceivers capable to switch on-the-fly between PM-QPSK and HEXA when channel propagation degrades. It also appears as a possible direct competitor of PM-QPSK, especially over NZDSF fiber and uncompensated links.

Performance evaluation of coherent WDM PS-QPSK (HEXA) accounting for non-linear fiber propagation effects

We demonstrate 160-Gb/s PDM 16-QAM single channel transmission over the longest distance yet to be reported, of 3123.9 km. The coherent receiver employs a frequency offset compensator based on a digital PLL.

160-Gb/s polarization-multiplexed 16-QAM long-haul transmission over 3,123 km using digital coherent receiver with digital PLL based frequency offset compensator

We demonstrate transmission of a 100-Gbit/s 32-QAM dual-polarization signal over a 200-km dispersion-managed fiber link using a digital coherent receiver. The receiver sensitivity of −20 dBm at BER = 10−3 is obtained after 200-km transmission.

http://ieeexplore.ieee.org/iel5/5273784/5286960/05287199.pdf

200-km transmission of 100-Gbit/s 32-QAM dual-polarization signals using a digital coherent receiver

We demonstrate 1,073-km transmission of 640-Gbit/s dual-polarization QPSK signals using a digital coherent receiver with the time-division demultiplexing function. The bit rate-distance product is the highest among those reported in single-carrier coherent transmission systems.

http://ieeexplore.ieee.org/iel5/5273784/5395699/05395704.pdf

Straight-line 1,073-km transmission of 640-Gbit/s dual-polarization QPSK signals on a single carrier

We demonstrate 1,000-km transmission of a 160-Gbit/s QPSK signal, using a digital coherent receiver with the time-division demultiplexing function, and confirm the applicability of such a receiver to long-haul transmission systems for the first time.

http://ieeexplore.ieee.org/iel5/5273784/5286960/05287319.pdf

Masatoshi Usui

Papers

200-km transmission of 100-Gbit/s 32-QAM dual-polarization signals using a digital coherent receiver

Straight-line 1,073-km transmission of 640-Gbit/s dual-polarization QPSK signals on a single carrier

Transmission of 160-Gbit/s QPSK signals on a single carrier over 1,000 km using digital coherent receivers