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Spectrally efficient communication is studied for short-reach fiber-optic links with chromatic dispersion (CD) and receivers that employ direction-detection and oversampling. Achievable rates and symbol error probabilities are computed by using auxiliary channels that account for memory in the sampled symbol strings. Real-alphabet bipolar and complex-alphabet symmetric modulations are shown to achieve significant energy gains over classic intensity modulation. Moreover, frequency-domain raised-cosine (FD-RC) pulses outperform time-domain RC (TD-RC) pulses in terms of spectral efficiency for two scenarios. First, if one shares the spectrum with other users then inter-channel interference significantly reduces the TD-RC rates. Second, if there is a transmit filter to avoid interference then the detection complexity of FD-RC and TD-RC pulses is similar but FD-RC achieves higher rates. [ABSTRACT FROM AUTHOR]

We report an industry leading optical dense wavelength division multiplexing (DWDM) field trial with line rates per channel $\ge 1.66$ Tb/s using 130 GBaud dual-polarization probabilistic constellation shaping 256-ary quadrature amplitude modulation (DP-PCS256QAM) in a high capacity data center interconnect (DCI) scenario. This research trial was performed on 96.5 km of field-deployed standard single mode G.652 fiber infrastructure of Deutsche Telekom in Germany employing Erbium-doped fiber amplifier (EDFA)-only amplification. A total of 34 channels were transmitted with 150 GHz spacing for a total fiber capacity of 56.51 Tb/s and a spectral efficiency higher than 11bit/s/Hz. In the single-channel transmission scenario 1.71 Tb/s was achieved over the same link. In addition, we successfully demonstrate record net bitrates of 1.88 Tb/s in back-to-back (B2B) using 130 GBaud DP-PCS400QAM. [ABSTRACT FROM AUTHOR]

Intensity modulation and direct detection (IM/DD) together with pulse amplitude modulation (PAM) is a cost-efficient solution for intra-datacenter links. However, sophisticated digital signal processing (DSP) is inevitable to reach the demanded high data rates for these short-reach applications. In this article, we compare different DSP schemes that enable rates of 200 Gb/s/λ and beyond. Those schemes include Tomlinson–Harashima precoding, partial response signaling, Viterbi equalization and post-filtering together with Volterra nonlinear equalization. Extensive experimental measurements are shown in which the DSP approaches are compared at gross rates between 180 Gb/s and 300 Gb/s. The experiments are done in C-band for fiber links of up to 2 km length. As modulation formats, PAM4, PAM6, and PAM8 are considered. Net bit rates well over 200 Gb/s are shown for all formats at a range of 1 km single mode fiber using a transmission system consisting of currently available commercial components. The optimum DSP configuration as well as the best modulation format varies along the investigated data rates. The best solution is shown to change from partial response PAM4 for lower rates to PAM6 and PAM8 at high bit rates. [ABSTRACT FROM AUTHOR]

We successfully demonstrate 400 Gbit/s transmission at 1577 nm over an unamplified 40 km standard single-mode fiber (SSMF) link with 11-dB loss target. Commercially available high-bandwidth coherent driver modulator (HB-CDM) and high-bandwidth micro integrated coherent receiver (HB- $\mu $ ICR), designed for $C$ -band are used in combination with two TO-can packaged and thermally tuned low-cost $L$ -band laser sources. With the aid of a memory-less one sample/symbol nonlinear offline digital-signal processing (DSP) correcting for the nonlinear transfer curve of the driver and modulator we can maximize the transmitter optical power, which is critical for unamplified fiber applications. In addition, multistage carrier recovery enables stable performance also with the large phase noise of the used coherent laser source, originally part of an electro-absorption modulated laser module (EML) and designed for extremely price-sensitive passive optical network (PON) applications. [ABSTRACT FROM AUTHOR]

We assess the impact of phase noise on the bit error rate (BER) after forward error correction (FEC) decoding (post-FEC BER) and on the error distribution in the case of differential and nondifferential (ND) transmission. We show that the use of pilot symbols enables reliable ND transmission and relaxes the requirements on bit-interleaving, and therefore, on the end-to-end latency. Further, we provide guidelines for the design and choice of carrier recovery and FEC parameters to obtain good performance in typical scenarios. All presented results are achieved through the use of a high-speed system emulation platform based on field-programmable gate arrays and thus achieve high reliability even for very low post-FEC BER. [ABSTRACT FROM PUBLISHER]