The extension of elastic optical network (EON) technologies to multi-band transmission (MB-EON) promises enhanced spectral efficiency, greater throughput, and long-term cost benefits for telecom operators. However, designing such networks presents challenges, particularly in optimizing physical parameters like optical power and quality of transmission (QoT) across different frequency bands. This paper introduces a methodology for optimal span-by-span power allocation using two hyper-accelerated power optimization (HPO) modes: flat launch power (FLP) and flat received power (FRP). This methodology significantly accelerate network power optimization while ensuring service stability in scenarios such as changes in network parameters, QoT degradation due to aging, and network re-optimization or upgrading. Through a comprehensive comparison, we find that FRP notably improves signal flatness and GSNR/OSNR, particularly in the S-band, contributing to a network-wide throughput increase in the order of 12% to 75%. Additionally, we demonstrate that HPO applied to global power optimization is simpler and more cost-effective than when applied to local methods for large-scale networks.

In the evolution of optical networks, spectral efficiency (SE) enhancement has been the most cost-efficient and thus the main driver for capacity increase for decades. As a result, the development of optical transport systems has been focused on the$C$- and$L$-bands, where silica optical fiber exhibits the lowest attenuation, and erbium-doped fiber amplifiers provide an efficient solution to compensate for the optical loss. With a gradual maturity in the SE growth, however, the extension of the optical bandwidth beyond the$C + L$-band is expected to play a significant role in future capacity upgrades of optical networks and, thus, attract increasing research interests. In this article, we discuss the merits and challenges of ultrawideband optical transport systems and networks beyond conventional bands.

Wavelength-division multiplexing (WDM) has historically enabled the increase in the capacity of optical systems by progressively populating the existing optical bandwidth of erbium-doped fiber amplifiers (EDFAs) in the$C$-band. Nowadays, the number of channels—needed in optical systems—is approaching the maximum capacity of standard$C$-band EDFAs. As a result, the industry worked on novel approaches, such as the use of multicore fibers, the extension of the available spectrum of the$C$-band EDFAs, and the development of transmission systems covering$C$- and$L$-bands and beyond. In the context of continuous traffic growth, ultrawideband (UWB) WDM transmission systems appear as a promising technology to leverage the bandwidth of already deployed optical fiber infrastructure and sustain the traffic demand for the years to come. Since the pioneering demonstrations of UWB transmission a few years ago, long strides have been taken toward UWB technologies. In this review article, we discuss how the most recent advances in the design and fabrication of enabling devices, such as lasers, amplifiers, optical switches, and modulators, have improved the performance of UWB systems, paving the way to turn research demonstrations into future products. In addition, we also report on the advances in UWB optical fibers, such as the recently introduced nested antiresonant nodeless fibers (NANFs), whose future implementations could potentially provide up to 300-nm-wide bandwidth at less than 0.2 dB/km loss.

This paper presents Ring Optical Network (RingO), a wavelength-division-multiplexing (WDM), ring-based, optical packet network suitable for a high-capacity metro environment. We present three alternative architectural designs and elaborate on the effectiveness of optic with respect to electronic technologies, trying to identify an optimal mix. We present the design and prototyping of a simple but efficient access control protocol, based upon the equivalence of the proposed network architecture with input-buffering packet switches. We discuss the problem of node allocation to WDM channels, which can be viewed as a particular optical network design problem. We, finally, briefly illustrate the fault protection properties of the RingO architecture. The main contribution of this paper is the identification and experimental validation of an innovative optical network architecture, which is feasible and cost effective with technologies available today, and can be a valid alternative to more consolidated solutions in metro applications.

We present in this paper a novel accurate method to analyze the performance of an optical link where the amplified spontaneous emission noise, enhanced by a fiber nonlinear phenomenon called parametric gain, is the limiting factor. Our method allows us to compute the exact error probability given a generic noise spectral density at the input of a direct detection optical receiver, using arbitrary optical and electrical filters. We compare our results with those predicted using the standard Gaussian technique (based on the Q factor), showing that this approximation may lead to significant errors. Our method is then used to evaluate the impact of parametric gain on a realistic long-haul multiwavelength link operating at 10 Gb/s, showing both the system limitation imposed by this phenomenon and the inaccuracy of the Q factor method.

A novel method to evaluate the bit error rate (BER) in optical links is described. It analyzes systems limited by amplified spontaneous emission (ASE) noise, enhanced by the non-linear parametric gain (PG) effect, and allows one to compute the exact error probability, given a generic optical noise spectral density at the input of a direct detection optical receiver. The method has been employed to evaluate the impact of PG on a 10 Gb/s per channel long-haul multi-wavelength system. It has also been used to show how the system performance evaluation based on the Q-factor Gaussian approximation may lead to erroneous BER evaluations.

We study the effect of parametric gain in long-haul, optically amplified links. We started by introducing a formalism required to evaluate the spectral enhancement of amplified spontaneous emission noise due to the Kerr-effect non-linear interaction between the signal and noise. These results are then used to evaluate parametric gain-induced performance degradation on the system Q value. Finally we analyze long-haul links at 10 Gb/s using different dispersion compensation maps by evaluating the maximum reachable distance in each configuration. We show that less frequent dispersion compensation improves the system performance.

The fast-paced evolution of long-haul and high-bit-rate terrestrial and submarine optical transmission links requires powerful analysis tools that take into account all the relevant phenomena in the fiber. To provide such a tool, we developed a time-domain optical system simulation package, integrated in the TOPSIM simulation environment. The fiber simulation module makes use of the vector form of the propagation equations to account for the quasi-degenerate two-mode (the two polarizations) medium propagation characteristics. This way, all polarization-related effects and their interplay with the other linear and nonlinear phenomena in the fiber can be accurately modeled. In particular, the fiber third-order susceptivity, responsible for all major nonlinear effects, is expressed in its actual vector form, so that nonlinear polarization mode coupling could be accounted for. Conventional birefringence and PMD are generated using appropriate random models. A novel feature of the simulator is that it uses time-domain digital filters to simulate dispersion effects, as opposed to the usual FFT-based algorithms. This approach leads to more efficient computing for a wide range of bandwidth and dispersion values. We present the fiber simulation module in detail. As an example of the use of the simulation package, the analysis of a long-haul two-channel transoceanic WDM transmission system is presented.

For the first time, a solution to the problem of recovering and tracking the signal constellation at the receiver side for binary and octonary digital optical transmission systems employing the modulation of polarization (POLSK) is proposed and analyzed. The effect of two recovery algorithms on the system performance is evaluated in terms of power penalty induced at P(e)=10/sup -9/, acquisition and tracking speed, and hardware complexity. The results show that very small penalties are obtainable in practical situations by properly designing the recovery algorithms.

The implementation of optical packet-switched networks requires that the problems of resource contention, signalling and local and global synchronization be resolved. A possible optical solution to resource contention is based on the use of switching matrices suitably connected with optical delay lines. Signalling could be dealt with using subcarrier multiplexing of packet headers. Synchronization could take advantage of clock tone multiplexing techniques, digital processing for ultra-fast clock recovery, and new distributed techniques for global packet-slot alignment. To explore the practical feasibility and effectiveness of these key techniques, a consortium was formed among the University of Massachusetts, Stanford University, and GTE Laboratories. The consortium, funded by ARPA, has three main goals: investigating networking issues involved in optical contention resolution (University of Massachusetts), constructing an experimental contention-resolution optical (CRO) device (GTE Laboratories), and building a packet-switched optical network prototype employing a CRO and novel signaling/synchronization techniques (Stanford University). This paper describes the details of the project and provides an overview of the main results obtained so far.

Receiver structures for the direct detection of binary and multilevel digital optical modulation schemes employing the modulation of the state of polarization of light, or polarization shift keying (POLSK), are proposed and accurately analyzed, in the presence of optical amplifier ASE noise and electrical receiver noise. A comprehensive set of results shows that the performance of the binary system is approximately 3 dB better than IM/DD (on peak optical power), and stays so for a wide range of optical filter bandwidths. As a somewhat unexpected result, the multilevel schemes show a lower sensitivity to the use of a wide optical filter than the binary one. As a consequence, transmitting 3 b/symbol on a cubic constellation on the Poincare sphere brings about virtually no penalty, whereas transmitting 2 b/symbol has a better performance than binary transmission, for even relatively low values of the optical filter bandwidth. A clear explanation of this phenomenon has been found. These results suggest that narrow-bandwidth and therefore low-dispersion, multilevel, POLSK transmission could be performed with no penalty. Together with the low excitation of nonlinear effects in the fiber that polarization modulation seems to ensure, these results make POLSK schemes look promising for very-long-haul transmission.>

The performance of optical coherent modulation schemes using the state of polarization of light as the modulating parameter (POLSK, POLarization Shift Keying) is analyzed, in the presence of laser phase noise. First, we compare three different analysis methods to account for the effects of phase noise in the binary case, and choose the one offering the best trade-off in terms of accuracy/complexity. Successively, we derive a tight upper bound to the performance of multilevel POLSK systems with postdetection filtering. Then, we include phase noise using the best method as tested in the binary case and extensively discuss the performance of binary and various multilevel POLSK constellations, optimized with respect to the IF filter bandwidth. The results show that binary POLSK has a very low sensitivity to phase noise and that multilevel POLSK is even less sensitive than the binary scheme.>

The application of the well-known technique of trellis coded modulation to coherent optical communications using polarization shift keying (POLSK) is described and analyzed. The resulting receiver is formed by a front-end which performs the heterodyne detection and the Stokes parameter extraction, cascaded with an electronic Viterbi processor operating the maximum likelihood estimate of the transmitted sequence. Results in terms of the error event probability using optimum as well as a simpler suboptimum branch metric show power gains of the order of 3-4 dB, at the expense of a reasonable increase in complexity, only concerning the processing in the electronic domain. These coding gains are not lost even in the presence of high levels of phase noise, to which POLSK in general is highly insensitive.>

This paper, together with a companion one [l], constitute a thorough presentation and analysis of a series of techniques grouped under the denomination “Polarization Spreading,” the intent of which is that of making the performance of a coherent optical receiver insensitive to the polarization transformations occurring along the optical fiber, without resorting to polarization compensation or control. The principle on which Polarization Spreading operates is that of spreading the signal power over different states of polarization, so that heterodyning of at least half of the optical incident bit energy is always ensured. The main obtained results concern (presented in [l]) a condition that guarantees the maximum heterodyned signal energy, some classes of spreading waveforms satisfying the above condition, the derivation of the structure and performance of optimum receivers in Gaussian noise; and, presented in this paper, the analysis of a suboptimum but easily implementable receiver and a detailed comparative analysis of the spectral broadening induced by the different spreading techniques. The results encompass most of the binary optical coherent modulation schemes proposed and experimented, such as ASK, FSK and DPSK.

Multilevel digital coherent optical modulation schemes based on the state of polarization of a fully polarized lightwave are proposed and analyzed. Based on the complete statistical characterization of the Stokes parameters, extracted through appropriate signal processing in the presence of shot and additive Gaussian noise, the optimum maximum likelihood receiver operating symbol by symbol is derived. The exact performance in terms of the average symbol error probability is found. Optimum constellations for the case of equipower 4, 8, 16 and 32 signals are found on the basis of the minimization of the error probability for a given average power. Their performance turns out to be promising as compared to other standard modulation techniques. The spectral analysis of polarization modulated signals is presented. A new receiver structure, which solves the problem of the excess penalties incurred in the presence of channel dichroism, is proposed and analyzed.>

Presents an analysis of a series of techniques grouped under the denomination "polarization spreading", the intent of which is that of making the performance of a coherent optical receiver insensitive to the polarization transformations occurring along the optical fiber, without resorting to polarization compensation or control. The principle on which Polarization spreading operates is that of spreading the signal power over different states of polarization, so that heterodyning of at least half of the optical incident bit energy is always ensured. The main results obtained concern a condition that guarantees the maximum heterodyned signal energy, some classes of spreading waveforms satisfying the above condition, the derivation of the structure and the performance of optimum receivers in Gaussian noise. The results encompass most of the binary optical coherent modulation schemes proposed and experimented, such as ASK, FSK and DPSK.>

The goals and basic node configuration of STARNET, an optical broadband local area network based on a physical passive star topology, are presented. Over a single physical network, STARNET offers all users both a moderate-speed packet network and a high-speed WDM circuit interconnect. Several topological and protocol solutions based on these two data transport facilities are available to the users. An ongoing experimental effort aimed at the realization of a STARNET prototype is described. The prototype nodes are FDDI and SONET OC-48 data-format-compatible. The first four network layers will be fully implemented and the nodes will serve high performance workstations.>

A rigorous analysis of digital coherent optical modulation schemes using the state of polarization as the modulating parameter is presented. The analysis obtains the exact performance of all the polarization-based modulation schemes proposed in the literature so far, including a differential demodulation scheme, named DPOLSK, which does not require either electrooptic or electronic polarization tracking. Preliminary results involving multilevel transmission schemes based on the state of polarization are introduced. A spectral analysis of POLSK signals is also proposed.>