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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. [ABSTRACT FROM AUTHOR]

A low complexity digital signal processing architecture for dual-polarization coherent detection is presented. It synchronizes impairments in the frequency domain and uses synergies between the filtering processing stages to minimize overall complexity. We show how chromatic dispersion, skew, carrier frequency offset, timing error, and the state of polarization can be mitigated with a single filtering stage in the frequency domain. The error estimation in the frequency domain is based on the modified Godard algorithm, which calculates the clock tone with less than two samples per symbol and small timing jitter. The synchronization in the frequency domain is independent of the modulation format and therefore a good candidate for higher order modulation formats and so the synchronization of probabilistic shaped (PS) signals based on a high cardinality rectangular QAM format. We show the synchronization of PS polarization-division multiplexed (PDM)-64QAM signals with a symbol rate of 42.7 GBd in the frequency domain. The simulative results for the influence of the FFT size and the number of FFT blocks used for the error estimation are shown. Finally, we show experimental results for four different probabilistic shapings in back-to-back and transmission over 300 km, which are synchronized with the introduced digital signal processing (DSP). [ABSTRACT FROM AUTHOR]

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 noninteger 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 Gb/s (4QAM), 90 Gb/s (4/16QAM), or 120 Gb/s (16QAM) sampled with 32 GSa/s and demodulate one of the subcarriers at a time. Transmission of 300 km through standard single mode fiber is demonstrated with a BER below the soft-decision forward error correction limit. [ABSTRACT FROM AUTHOR]

In this letter, we report on the advances toward the integration of our developed continuous variables (CV) quantum key distribution (QKD) system in existing optical infrastructure and wavelength division multiplexed (WDM) networks. First, we investigate the tolerance of the CV-QKD system to spontaneous Raman scattering (SRS) noise, the latter being the most dominant impairment in a WDM co-existence environment for QKD. In particular, we investigate by experiment the impact of a WDM 10×1010\times 10 Gb/s ON–OFF-keying signal in terms of induced SRS noise in the QKD channel. The spontaneous SRS noise influence is assessed for different transmission scenarios, i.e., for various optical launch powers of the WDM signal, and for different transmission links of 20, 40, 60, and 80 km. Based on the experimental data and on the measured system’s parameters, we estimate the key rates and reach capabilities of the proposed CV-QKD system. The scheme supports a key rate of 90 kbit/s over 20 km, for an ideal QKD system multiplexed with 2-mW optical power. A step further, we demonstrate for first time the use of the aforementioned CV-QKD system to encrypt a 10GE client service over deployable optical transport network legacy equipment over 20 km. Our results prove the feasibility of the integration of our proposed scheme with legacy telecom equipment in existing WDM optical networks. [ABSTRACT FROM AUTHOR]

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 x 10-3 were achieved. [ABSTRACT FROM AUTHOR]

A timing recovery algorithm is introduced that operates with less than two samples per symbol and provides an enormous complexity reduction. The complexity reduction is due to a synergy with the already existing Fourier transforms in a coherent receiver, an avoidance of terms that are dominated by noise, and a complete elimination of multiplications. A simulation and an experiment with a single carrier modulation format show that the inherent timing jitter is, despite of the significant complexity reduction, comparable with the state of the art, and in particular outperforms the Godard algorithm for low roll-off factors. In addition, it is one of the few algorithms that operates with less than two samples per symbol in the frequency domain, and thus enables the lowest complexity in a receiver. [ABSTRACT FROM AUTHOR]

Complementing plasmonic slot waveguides with highly nonlinear organic materials has rendered a new generation of ultracompact active nanophotonic components that are redefining the state of the art. In this paper, we review the fundamentals of this so-called plasmonic–organic–hybrid (POH) platform. Starting from simple phase shifters to the most compact $IQ$ modulators, we introduce key devices of high-speed data communications. For instance, all-plasmonic Mach–Zehnder modulators (MZMs) are reviewed and long-term prospects are discussed. This kind of modulator already features unique properties such as a small footprint ( <$ 20 \mu$m ), a large electro–optic bandwidth ( >$ 110 GHz), a small energy consumption ( \sim$25 fJ/b), a large extinction ratio ( >$ 25 dB) in combination with a record small voltage-length product of 40 V \mu$ m. Finally, as an example for seamless integration we introduce novel plasmonic . This demonstration ultimately shows how plasmonics can be used to control both phase and amplitude of an optical carrier on the microscale with reasonably low losses. [ABSTRACT FROM AUTHOR]

Software-defined transceivers offer flexibility, increased resilience to channel impairments, and an upgrade path for the future transmission systems. Such transceivers have been discussed in the literature for several years and are now about to be established in long-haul optical communications. In access networks, however, the circumstances are different. Here, a great variety of transceiver and network architectures has been developed. The hardware implementations impose various limitations on the benefits that are usually associated with software-defined transceivers. So the question is: Will software-defined transceivers be of equal importance in dynamic access networks? And, as fundamental limitations mainly originate in the modulation and detection techniques, which hardware implementations would be most promising for software-defined transceivers? [ABSTRACT FROM PUBLISHER]

Reflective semiconductor optical amplifier fiber cavity lasers (RSOA-FCLs) are appealing, colorless, self-seeded, self-tuning and cost-efficient upstream transmitters. They are of interest for wavelength division multiplexed passive optical networks (WDM-PONs) based links. In this paper, we compare RSOA-FCLs with alternative colorless sources, namely the amplified spontaneous emission (ASE) spectrum-sliced and the externally seeded RSOAs. We compare the differences in output power, signal-to-noise ratio (SNR), relative intensity noise (RIN), frequency response and transmission characteristics of these three sources. It is shown that an RSOA-FCL offers a higher output power over an ASE spectrum-sliced source with SNR, RIN and frequency response characteristics halfway between an ASE spectrum-sliced and a more expensive externally seeded RSOA. The results show that the RSOA-FCL is a cost-efficient WDM-PON upstream source, borrowing simplicity and cost-efficiency from ASE spectrum slicing with characteristics that are, in many instances, good enough to perform short-haul transmission. To substantiate our statement and to quantitatively compare the potential of the three schemes, we perform data transmission experiments at 5 and 10 Gbit/s. [ABSTRACT FROM AUTHOR]

Optical frequency combs have the potential to revolutionize terabit communications. The generation of Kerr combs in nonlinear microresonators is particularly promising, enabling line spacings of tens of gigahertz. However, such combs may exhibit strong phase noise, which has made high-speed data transmission impossible up to now. Here, we demonstrate that systematic adjustment of the pump conditions for low phase noise enables coherent data transmission with advanced modulation formats that pose stringent requirements on the spectral purity of the comb. In a first experiment, we encode a data stream of 392 Gbit s−1 on a Kerr comb using quadrature phase-shift keying and 16-state quadrature amplitude modulation. A second experiment demonstrates feedback stabilization of the comb and transmission of a 1.44 Tbit s-1 data stream over up to 300 km. The results show that Kerr combs meet the highly demanding requirements of coherent communications and thus offer an attractive route towards chip-scale terabit-per-second transceivers. [ABSTRACT FROM AUTHOR]

A comb generator based on feeding a single dual drive Mach–Zehnder modulator with a sinusoidal radio frequency (RF) at one arm and its double frequency at the other arm is demonstrated. Our comb generator benefits from the superposition of optical subcarriers generated by the fundamental and its second harmonic. We demonstrate flexibility in center wavelength tunability, subcarrier spacing, and subcarrier count. For a fundamental frequency at, e.g., 6.25 GHz, our comb generator can produce 9, 5, 4, or 3 optical subcarriers with a spectral flatness of <1.2~dB. We successfully demonstrate to the best of our knowledge, the generation of the largest number of comblines requiring the lowest drive signal with the least components within the field of RF-generated combs. [ABSTRACT FROM PUBLISHER]

We demonstrate single-laser 32.5 Tbit/s 16QAM Nyquist wavelength division multiplexing transmission over a total length of 227 km of SMF-28 without optical dispersion compensation. A number of 325 optical carriers is derived from a single laser and encoded with dual-polarization 16QAM data using sinc-shaped Nyquist pulses. As we use no guard bands, the carriers have a spacing of 12.5 GHz equal to the symbol rate or Nyquist bandwidth of the data. We achieve a net spectral efficiency of 6.4 bit/s/Hz using a software-defined transmitter, which generates the electric drive signals for the electro-optic modulator in real time. [ABSTRACT FROM PUBLISHER]