In this paper we will give an insight to the FABULOUS European Project, pertaining to the 7thFramework Program, showing a self-coherent passive optical network that employs Frequency Division Multiplexing and is compatible with legacy infrastructures and NG-PON2 power budget specifications, while exceeding them in terms of bit-rate. FABULOUS also envisions an innovative Optical Network Unit, based on a reflective Mach-Zehnder modulator, that is suitable for full integration in silicon-photonics, for realizing low-cost customer premises equipment, indispensable for a massive deployment of the solution. The novelty of this work compared to previous papers in the same areas is in focusing on different possible applications having different physical layer requirements, including the recent trend that propose high-capacity PON as an alternative solution for next-generation Local Area Network.

The physical characteristics of microring resonator switching devices are thoroughly analyzed using a model based on the field coupling matrix theory. The spectral response and insertion loss properties of these switching elements are simulated using the developed model. Results show that by cascading three microring resonators it is possible to achieve flat-top passband widths ranging from 6.25 GHz to 3 THz, while having insertion losses compatible with the use in flexible-grid optical communication networks. In light of a potential use of these devices in the design of a scalable flexible wavelength selective switch, the architecture of simple optical switches with limited functionalities is discussed.

Interconnection networks must transport an always increasing information density and connect a rising number of processing units. Electronic technologies have been able to sustain the traffic growth rate, but are getting close to their physical limits. In this context, optical interconnection networks are becoming progressively more attractive, especially because new photonic devices can be directly integrated in CMOS technology. Indeed, interest in microring resonators as switching components is rising, but their usability in full optical interconnection architectures is still limited by their physical characteristics. Indeed, differently from classical devices used for switching, switching elements based on microring resonators exhibit asymmetric power losses depending on the output ports input signals are directed to. In this paper, we study classical interconnection architectures such as crossbar, Benes and Clos networks exploiting microring resonators as building blocks. Since classical interconnection networks lack either scalability or complexity, we propose two new architectures to improve performance of microring based interconnection networks while keeping a reasonable complexity.

The design of fabrics for Terabit packet switches and routers needs to consider the limitations imposed by the electronic technology; in particular, more and more attention has to be paid to information density and to power consumption and dissipation, as well as to power supply and footprint requirements. These issues make more difficult to package a packet switch in one single rack of equipment; thus, optical links start being used to interconnect the line cards with the switching fabric. In this paper, we consider optical interconnection architectures that exploit wavelength agility at line cards to control switching decisions. The actual feasibility and physical layer scalability of this approach is analyzed by considering different optical fabric alternatives to interconnect the line cards. The main contribution of the paper is the characterization of these optical fabrics in terms of their power budget, and the analysis of the port count and of the aggregate bandwidth offered by these architectures to build Terabit packet switches.

Optical community has expressed a wide consensus over the idea that 1 mm poly-methil-meta-acrilate step-index fibres (PMMA SI-POF) can be a good candidate in future domotic networks and in edge networks, that is in the last part of access networks, due to their better mechanical behaviour and lower installation and handling costs with respect to conventional 50/125 or 62.5/125 multi-mode glass fibres. Current applications are anyway limited by relatively low transmission performances: up to now, the best performing commercial Ethernet transceivers using PMMA SI-POF are able to reach at the most 200 m at 10 Mb/s or 70 m at 100 Mb/s, thereby keeping these fibres in the niche of very-short reach applications, such as in the automotive market. A Prototype of a media converter for fully compliant 10 Mb/s Ethernet transmissions over PMMA SI-POF experimentally demonstrated the feasibility of >400 m long link, this length may open new applications to PMMA SI-POF. The 425-m record distance presented here has been achieved by both introducing a proprietary protocol implemented over a field programmable gate array platform and by a careful selection of (commercial) optoelectronic components. The prototype is to be considered as a proof-of-concept that PMMA SI-POF can be introduced in new areas such as the last part of access/edge networks or datacom applications in industrial automation or aircrafts/ships cabling. The 400-m distance is, for instance, the specification of an Italian fibre to the home operator for the last part of its access network architecture.

The WONDER project aims at designing and building a WDM packet-switched slotted ring network, with tunable transmitters and fixed receivers. An experimental prototype is under development at the laboratories of Politecnico di Torino. In this paper, we study two different strategies of slot synchronization for such networks: in the former, a slot synchronization signal is transmitted by the master station on a dedicated control wavelength; in the latter, slave nodes achieve slot synchronization aligning on data packets received from the master. Emphasis has been given to the architecture of the WONDER network. The performance of the two synchronization strategies, in terms of packet collision probability, has been evaluated by simulation. The technique based on transmitting a timing signal on a dedicated control wavelength resulted in achieving a better performance, although being more expensive due to need of an additional wavelength. However, the technique based on aligning on data packets received from the master should be not discarded, although attaining lower timing stability, especially if limiting the number of wavelengths and receivers is a strong requirement.

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.

In this paper, we present a novel mathematical investigation on the dispersion-limited optical communication channel. We tackle the problem using a comprehensive approach that is based on the optimization of the energy transfer from the input to the output of the channel. We solve the optimization problem deriving a fundamental integral equation, which we are able to solve analytically. We show that the dispersion-limited optical channel has a very interesting equivalence to the ideal lowpass filter. This equivalence allows us to derive new bounds on the maximum achievable bit rate on the channel with limited intersymbol interference (ISI). In particular, we demonstrate that by suitably increasing the memory of the modulator and using the optimal pulses derived in this paper, one can transmit with limited ISI over a channel with arbitrarily high dispersion.

Wavelength routed optical networks allow to design a logical topology, comprising lightpaths and routers, which is overlayed on the physical topology, comprising optical fibers and optical cross-connects, by solving a routing and wavelength assignment (RWA) problem. In this paper we extend the concept of lightpath to the one of super-lightpath, which uses a simple bit level time division multiplexing that can be directly implemented in the optical domain, to split the wavelength bandwidth among more than one traffic flow. This allows to design logical topologies with an increased number of logical links, thus reducing the average distance among nodes, i.e., the number of electro-optic and opto-electronic conversions, and the traffic congestion on logical links. At the same time, this reduces the number of wavelengths required to solve the RWA problem. Being the super-lightpath RWA problem computationally intractable, we propose two heuristics which show that the number of wavelengths required to overlay the same logical topology on the same physical topology is reduced by more that 65% using super-lightpaths.

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 experimental demonstration of MOSAIC, a reconfigurable WDM add/drop network with subcarrier multiplexed control, is presented. The MOSAIC network implements the optical layer protocol to support bit-rate transparent multichannel lightpaths. Two types of add/drop multiplexers are implemented and combined in a three-node experiment. Multihop lightpaths are established giving an end-to-end bit error rate of better than 10/sup -9/ at 1.2 Gbps. The reconfigurable add/drop multiplexer is based on a novel dilated 2/spl times/2 acoustooptic filter switch crossconnect and an analog optoelectronic crossconnect that drives a ten-wavelength laser array transmitter up to 2.5 Gbps per wavelength. The fixed wavelength add/drop multiplexer utilizes a fast digitally tunable laser transmitter. Both add/drop multiplexers support bit-rate transparent 2R optoelectronic regeneration as well as wavelength translation. Subcarrier multiplexing on each wavelength is used to support channel state monitoring and channel equalization as well as transmission of digital network control information. Systems experiments demonstrate cascaded 2R optoelectronic regeneration with wavelength translation and cascaded multichannel optical switching with up to seven hops. It is shown that combining cascaded 2R optoelectronic regeneration with cascaded multichannel optical switching can be used to balance jitter accumulation and amplified spontaneous emission generated amplitude noise to yield high signal-to-noise ratio for lightpaths.

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.

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.>