We propose and demonstrate a new low-complexity hardware architecture and digital signal processing (DSP) implementation for coherent reception of Nyquist frequency division multiplexed (Nyquist-FDM, digital subcarrier multiplexing) signals in real-time. Key to achieve lowest complexity is the combination of an optimized frequency domain and time domain processing block. In the frequency domain processing we combine subcarrier equalization and timing recovery with a non-integer oversampling ratio of 16/15. In the time domain, we take advantage of polar coordinate processing for the carrier recovery to avoid complex multiplications. The receiver is optimized for flexible operation and allows the adaption of filter coefficients and modulation format between 4QAM, hybrid 4/16QAM, and 16QAM within one clock cycle. The efficiency of the DSP is demonstrated by a real-time coherent receiver implementation on a single FPGA and is experimentally evaluated. Despite of the limited hardware resources, the receiver can detect a 30 GBd Nyquist-FDM signal with four subcarriers and a net data rate of 60 Gbit/s (4QAM), 90 Gbit/s (4/16QAM), or 120 Gbit/s (16QAM) sampled with 32 GSa/s and demodulate one of the subcarriers at a time. Transmission of 300 km through SSMF is demonstrated with a BER below the soft-decision forward error correction (SD-FEC) limit.

Over the past fifty years, telecommunications has transformed, in an unprecedented manner, the way we live, work and communicate. For telecommunications, fixed networks are the one pillar and wireless networks the other. The wireless networks and their generations have been extensively investigated in the literature; however, the fixed networks lack a consistent exploration of their evolution. For this purpose, our motivation is to present a review of the evolution of fixed networks in a holistic manner, from various different perspectives, which can assist engineers and students to understand, in a better way, how broadband networks developed and the main features of the current networking environment. Specifically, in this review, we aim to shed light on the most important technologies, standards and milestones of the fixed networks from various perspectives, such as the service perspective, the networking perspective (both access and core part) and the physical layer perspective. Our study follows the timeline of the five generations of fixed networks defined by the European Telecommunications Standards Institute (ETSI) F5G group and discusses the key achievements and limitations of each generation for each different infrastructure layer and segment, designating the most important issues for the most widely-adopted technologies and standards. Finally, our analysis helps to reveal the technical challenges that need to be addressed by the fixed telecom network community, such as energy efficiency, capacity scaling, cost-efficiency, etc., while also revealing potential future directions.

We report on an optical chip-to-chip interconnect solution, thereby demonstrating plasmonics as a solution for ultra-dense, high-speed short-reach communications. The interconnect comprises a densely integrated plasmonic Mach-Zehnder modulator array that is packaged with standard driving electronics. On the receiver side, a germanium photodetector array is integrated with trans-impedance amplifiers. A multicore fiber provides a compact optical interface to the array. We demonstrate 4 × 20 Gb/s on-off keying signaling with direct detection.

We present a demonstration of software defined networking (SDN) services utilizing quantum key distribution (QKD) technology, fully integrated with standard telecommunication network connecting production facilities of Telefonica in Madrid. All communications “co-propagate” over the same fiber infrastructure.

We present a comparative study of the capacity increase brought by bit- and power-loading discrete multi-tone (DMT) modulation for low-cost colorless transmitters. Three interesting reflective semiconductor optical amplifier (RSOA) based colorless transmitter configurations are compared: First, an amplified spontaneous emission (ASE) spectrum-sliced source; second, a self-seeded RSOA fiber cavity laser (FCL) and third, an externally seeded RSOA. With bit- and power-loaded DMT, we report record high line rates of 6.25, 20.1 and 30.7 Gbit/s and line rates of 4.17, 10.1 and 24.5 Gbit/s in a back-to-back and in a 25 km nonzero dispersion shifted fiber (NZDSF) transmission experiments for the three transmitter configurations, respectively. In all the experiments, BER (bit error ratios) below an FEC (forward error correction) limit of 7.5 × 10⁻³ were achieved.