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We demonstrate concepts and results of a field trial for a flexible-rate passive optical network (FLCS-PON), which delivers bitrates up to 100 Gbit/s and allows for adaptations in the transmission method to match the users’ channel conditions and optimize throughput. FLCS-PON builds on top of the hardware ecosystem that will be developed for ITU-T 50 Gbit/s PON and employs three new ingredients: optical network unit (ONU) grouping, flexible modulation format, and flexible forward error correction (FEC) code rate. Together, these techniques take advantage of the optical distribution network (ODN) statistics to realize a system capable of more than twofold throughput increase compared to the upcoming 50 Gbit/s PON, but still able to support a full array of deployed fiber edge cases, which are problematic for legacy PONs. In this paper we explain the concepts behind enabling techniques of FLCS-PON. We then report on a field trial over a deployed fiber infrastructure, using a system consisting of one FLCS-PON OLT and two ONUs. We report both pre- and post-forward-error-correction (post-FEC) performance of our system, demonstrating achievable net bitrate over an operator's fiber infrastructure. We realize a downlink transmission at double the speed of ITU-T 50 Gbit/s PON for ONUs exhibiting lower optical path loss (OPL), while simultaneously continue to support ONUs at high OPLs. We additionally realize a record-high 31.5 dB loss budget for 100 Gbit/s transmission using a direct-detection ONU with an optical preamplifier. [ABSTRACT FROM AUTHOR]

Heterodyne detection based on a single-ended photodetector is of great interest to simplify the receiver frontend complexity compared to a full coherent one, while retaining the ability of digital chromatic dispersion (CD) compensation. Nevertheless, single-ended heterodyne detection schemes typically require a transmitter, which has similar complexity as in coherent systems. Moreover, a receiver bandwidth equal to at least the symbol rate of the signal is required for the complex-valued signal recovery when using a single-ended photodetector. In this article, we study a novel heterodyne detection scheme, which allows to use a simple transmitter structure, and to reduce the receiver bandwidth to a value well below the symbol rate, while supporting digital CD compensation. In our experiment, a real-valued signal originates from a single-drive Mach–Zehnder modulator at the transmitter. A bandwidth-limited receiver suppresses one sideband of the incoming signal, however the receiver digital signal processing (DSP) reconstructs the missing sideband based on the Hermitian symmetry of a real-valued signal spectrum. A receiver bandwidth slightly larger than half of the symbol rate is required. With our novel DSP, we successfully recover 60 Gbaud PAM-4 signal after 80 km of fiber transmission in C-band, using 33 GHz electrical bandwidth at both transmitter and receiver, without optical filtering or amplification. [ABSTRACT FROM AUTHOR]

A time-reversal array in multimode fiber is proposed for lossless remotely controlled switching using passive optical splitters. The signal to be transmitted is digitally predistorted so that it is routed through the physical layer in order to arrive at only one receiver in an array. The system performance in the presence of an additive white Gaussian noise, modal group delay, and timing error is investigated numerically for single-mode fiber and 10-mode fiber. Focusing using a two-transmitter array and 44 km of single-mode fiber is demonstrated experimentally for 3-GBd QPSK signals with a bit error rate below the forward error correction limit. [ABSTRACT FROM PUBLISHER]

The aim of cognition in optical networks is to introduce intelligence into the control plane that allows for autonomous end-to-end performance optimization and minimization of required human intervention, particularly targeted at heterogeneous network scenarios. A cognitive network observes, learns, and makes informed decisions based on its current status and knowledge about past decisions and their results. To test the operation of cognitive algorithms in real time, we created the first operational testbed of a cognitive optical network based on the Cognitive Heterogeneous Reconfigurable Optical Network (CHRON) architecture. In this experiment, an intelligent control plane, enabled by a cognitive decision system (CDS), was successfully combined with a flexible data plane. The testbed was used to test and validate different scenarios, demonstrating benefits obtained by network cognition, particularly lightpath establishment and a teardown scenario, improved failure restoration time, cognitive virtual topology reconfiguration, and a modulation format change. [ABSTRACT FROM PUBLISHER]

In this paper, joint estimation of carrier frequency, phase, signal means and noise variance, in a maximum likelihood sense, is performed iteratively by employing expectation maximization. The parameter estimation is soft decision driven and allows joint carrier synchronization and data detection. The algorithm is tested in a mixed line rate optical transmission scenario employing dual polarization 448 Gb/s 16-QAM signal surrounded by eight on-off keying channels in a 50 GHz grid. It is shown that joint carrier synchronization and data detection are more robust towards optical transmitter impairments and nonlinear phase noise, compared to digital phase-locked loop (PLL) followed by hard decisions. Additionally, soft decision driven joint carrier synchronization and detection offers an improvement of 0.5 dB in terms of input power compared to hard decision digital PLL based carrier synchronization and demodulation. [ABSTRACT FROM PUBLISHER]

High order modulation formats allow to reach higher spectral efficiency and data rate. However, their practical implementation is limited by their reduced tolerance to noise and to the optical signal power that can be launched into the fiber without generating excessive nonlinear signal distortions. In this paper, it is demonstrated that Turbo Equalization routines can be used to mitigate performance degradations stemming from optical fiber propagation effects both in optical fiber dispersion managed and unmanaged coherent detection links. The effectiveness of this solution is analyzed both numerically and experimentally for different transmission systems. [ABSTRACT FROM PUBLISHER]

The flexibility and elasticity of the spectrum is an important topic today. As the capacity of deployed fiber-optic systems is becoming scarce, it is vital to shift towards solutions ensuring higher spectral efficiency. Working in this direction, we report an extensive experimental study on adaptive allocation of superchannels in spectrum-flexible heterogeneous optical network. In total, three superchannels were transmitted. Two 5-subcarrier 14-GHz-spaced, 14 Gbaud, polarization-division-multiplexed (PDM) quadrature-phase-shift-keyed (QPSK) superchannels were separated by a spectral gap, the band of interest (BOI). The bandwidth of the BOI was varied. The BOI was subsequently filled with another superchannel, constituted by a different number of either 14 Gbaud PDM-QPSK or PDM-16-ary quadrature amplitude modulation (16-QAM) subcarriers. The optical signal-to-noise ratio (OSNR) for transmission of the subcarriers inserted into the BOI, depending on the modulation format, subcarrier count and spacing to the neighboring superchannels, was extracted through experimental implementation of different scenarios. The obtained values were interpolated to yield the required OSNR necessary to maintain a 1×10−3 bit error rate of the central BOI subcarrier. The results provide a rule of thumb that can be exploited in resource allocation mechanisms of future spectrum-flexible optical networks. [ABSTRACT FROM PUBLISHER]