Optical-electrical-optical Research Articles

Optical matrix computing for optical forward error correction encoding

Forward error correction (FEC) has been widely used in today's communication systems, implemented by electronics. For optical communications, on-the-fly optical processing is highly desired for reduced optical-electrical-optical (OEO) conversions, so as to reduce the latency and cost. In this work, we present a proof-of-concept study of an optical FEC encoding method based on optical matrix computing by wavelength-division multiplexing (WDM) with time-wavelength interleaved manipulation. The optical FEC encoder realized by optical fiber devices features nearly equivalent net encoding gain compared with the theoretical electrical encoder. The experimental results indicate effective error correction, with 2-dB net gain in on-off keying (OOK) transmission at 20 Gb/s, supporting the realization of transmission-computing-merged systems. Meanwhile, the proposed method also supports the whole realization of FEC with both encoding and decoding.

Energy-efficient regeneration routing in satellite optical networks under translucent optical payload architectures.

The translucent optical payload architecture is most economical and feasible for optical switching in the satellite optical network (SON) using laser inter-satellite links (LISLs), where the wavelength division multiplexing (WDM) technology enables lightpaths to transparently pass through relay satellites, minimizing on-board processing. For the long-distance lightpath in SONs, lightpath regeneration is necessary to ensure the acceptable quality of transmission (QoT), where optical-electrical-optical (OEO) conversion causes non-negligible energy consumption. The rechargeable battery is an important component for low-earth-orbit (LEO) satellites, and unrestrained use batteries at a deep depth of discharge (DOD) will accelerate battery aging and shorten satellite lifetime, causing extremely high expenditure costs. How to improve energy efficiency in lightpath regeneration is a key problem in SONs, which has no related studies. This paper proposes energy-efficient regeneration routing (EE-RR) in SONs under translucent optical payload architectures, which is to reduce the battery life consumption of lightpath regeneration. We define the maximum bypass hops (MBH) to ensure the bit error rate (BER) requirement of lightpaths in SONs, considering the noise accumulation of amplifier spontaneous emission (ASE) and Doppler shift (DS) crosstalk. Two greedy baselines are proposed for EE-RR, which are the regeneration routing scheme minimizing the number of regeneration nodes (RRS-MRN) and the regeneration routing scheme minimizing single satellite's battery life consumption (RRS-MBL), respectively. Based on two greedy baselines, the regeneration routing scheme using genetic algorithms (RRSGA) is developed to improve the optimization ability of EE-RR. To our knowledge, this is the first study to propose taking battery aging into account in lightpath regeneration in SONs. Through numerical simulation, we find that blindly reducing the number of regeneration nodes in lightpaths may not reduce overall battery life consumption, and RRSGA can effectively reduce battery life consumption of lightpath regeneration in SONs.

Electrical Regeneration for Long-Haul Fiber-Optic Time and Frequency Distribution Systems.

In recent years fiber-optic-based long-haul installations for time and frequency (T&F) distribution have become operational at various sites. The common practice to cope with large attenuation of long fiber path is to use bidirectional optical amplifiers. This, however, becomes insufficient in case of very long links and/or long spans between amplifiers, because of unavoidable deterioration of the signal-to-noise ratio (SNR). In this article, we present a solution where the optical signal amplification is combined with optical-electrical-optical (OEO) regeneration, performed in a few points along the link. We analyze the impact of replacing some optical amplifiers with OEOs and demonstrate the resulting improvement in terms of SNR of the received optical signal and the phase noise at the output of the T&F distribution system. Laboratory experiments performed with both spooled and metropolitan-area fibers (total length up to 900 km) confirmed the theoretical predictions and showed that placing the OEO regenerators in appropriate points along the link allows reaching the required SNR.

Design of Novel Fiber Optical Flexible Routing System

In this paper, we propose a new versatile routing device that utilizes arrayed waveguide gratings (AWGs), optical switches, and optical circulators to implement reconfigurable optical add/drop multiplexers (ROADMs), optical interleavers, and optical cross-connect (OXC). With the development of dense wavelength division multiplexing (DWDM) technology, ROADM and OXC technologies have also been put into practical use. Thus, the optical signal can be routed directly in the optical network according to its wavelength without the need for optical-electrical-optical (OEO) conversion. Although different optical network units (ONUs) have different bandwidth requirements, the use of optical interleavers has successfully solved the connection problem between old and new systems. According to the numerical experiments of static characteristics, the proposed routing device can effectively implement three different functionalities, thereby providing greater flexibility for fiber optic network applications.

Prospects and research issues in multi-dimensional all optical networks

Research into all optical network (AON) technology has been ongoing over the past decade, and new features are constantly being developed. The advantages of AON include large-bandwidth provisioning, low-latency transmission and low energy consumption. The basic concept underlying AON is transmission of data signals entirely through the optical domain from source to destination nodes, with no optical-electrical-optical (O-E-O) conversion at intermediate nodes. The technologies used to implement AON have undergone a series of evolutions, which encompass time division multiplexing (TDM), frequency division multiplexing (FDM), and space division multiplexing (SDM). Multi-dimensional AON (MD-AON), which leads the trend of AONs future architecture, provides a vibrant state for emerging applications such as cloud computing and Internet of Things (IoT). In this article, we review the evolution of AON architectures based on the different all optical switching and multiplexing technologies (i.e., TDM, FDM, and SDM), which is one of the main areas of focus in this article. The other main area is detailed discussion of implementations such as data plane and control plane technologies as well as resource optimization technologies for realizing AON. We also introduce several AON testbeds with their compositions and functions, and some potential application scenarios that can be implemented based on these testbeds

Improved Performance Robustness of DSP-Enabled Flexible ROADMs Free from Optical Filters and O-E-O Conversions

Utilizing Hilbert-pair-based digital filtering, intensity modulation, and passive optical coupling, digital signal processing (DSP) enabled flexible reconfigurable optical add/drop multiplexers (ROADMs) are reported, which are free from optical filters and optical-electrical-optical (O-E-O) conversions and offer excellent flexibility, colorlessness, gridlessness, contentionlessness, adaptability, and transparency to physical-layer network characteristics. In this paper, the ROADM performance robustness against variations in numerous network design aspects is, for the first time to the best of our knowledge, extensively explored in intensity-modulation- and direct-detection-based optical network nodes. Numerical results show that DSPs not only enable the ROADMs to dynamically and flexibly perform add/drop operations at wavelength, subwavelength, and spectrally overlapped orthogonal subband levels but also considerably improve the ROADM performance robustness against variations in modulation formats, transmission system characteristics/impairments, and terminal equipment configurations.

Energy-Efficient Cascaded Bit-Interleaved Converged Optical Access/In-Building Network Protocol

This paper proposes the cascaded bitinterleaved optical network protocol, an energy-efficient solution aiming at low power consumption in converged optical access/in-building networks while providing high data rates to end users, and a novel network architecture for optical access/in-building networks. In the proposed network architecture, optical–electrical–optical (OEO) regeneration is employed at the interface between access and in-building networks. The downstream frames are generated in the central office using a two-stage bitinterleaving scheme. In the downstream direction, the network nodes only process the data destined for them at a lower clock rate than that of the aggregate passive optical network (PON). In the upstream direction, no word alignment or decoding is performed in the intermediate nodes. Simulation and experimental results show that significant reduction in the power consumption of access/in-building networks can be achieved when the proposed cascaded bit-interleaved protocol is employed in conjunction with the proposed network architecture.

Attack-aware planning of transparent optical networks

This work presents algorithms for the planning phase of wavelength division multiplexed (WDM) optical networks considering the impact of physical layer attacks. Since the signals in transparent WDM networks are transmitted all-optically without undergoing any Optical–Electrical–Optical (OEO) conversions, these networks are vulnerable to high-power jamming attacks. Due to crosstalk-induced interactions among different connections, malicious high-power signals can potentially spread widely in the network. To this end, it is necessary to plan an optical network in a way that the spread of an attack is minimized. In this work novel Integer Linear Programming (ILP) formulations are proposed that address the problem of routing and wavelength assignment (RWA) with the objective to minimize the propagation of the introduced high-power malicious signals. The physical layer attack propagation is modeled as interactions among connections through in-band and out-of-band channel crosstalk. In addition, Linear Programming (LP) relaxation techniques and heuristic algorithms are used to handle larger network instances. Performance results indicate that the proposed algorithms perform close to the traditional RWA algorithms in terms of total wavelength utilization of the network, while at the same time providing security against high-power jamming attacks by minimizing the total number of in-band and out-of-band lightpath interactions.

Survivable power efficiency oriented integrated grooming in green networks

The wide interests in the power savings of IP over wavelength-division-multiplexing (WDM) optical networks have recently risen in both academic and industrial communities. In an effort to tackle this problem, the hybrid grooming (traffic grooming along with an optical bypass) approach has been presented to reduce the power consumed by the entire network infrastructure, including the transmission ports of routers and optical-electrical-optical (OEO) conversions. However, the related works pay little or no attention to the power consumed to ensure the resiliency of the overall network. Meanwhile, the power consumed by components used for establishing lightpaths is not simultaneously taken into account. One survivable network with the higher power efficiency thereby save more power with hybrid grooming, require the lower power consumption of establishing lightpaths and exhibit the shorter recovery time. For the first time, this paper proposes the evaluating models of both survivable power ratio and protection switching time. We subsequently compare two green and survivable grooming heuristics, known as Single-hop Survivable Grooming with considering Power Efficiency (SSGPE) and Multi-hop Survivable Grooming with considering Power Efficiency (MSGPE). Simulation results demonstrate that, MSGPE obtains the higher power efficiency and resiliency although it has the slightly higher time complexity in comparison to SSGPE. Furthermore, it is effective to exploiting waveband merging in our MSGPE to form integrated grooming for further port savings.

A Novel Offline PLI-RWA and Hybrid Node Architecture for Zero Blocking and Time Delay Reduction in Translucent Optical WDM Networks

In this paper, we contrive a model that underpins the offline Physical Layer Impairment-Routing and Wavelength Assignment (PLI-RWA) issue in translucent networks. We introduce an innovative PLI-Signal Quality Aware RWA (PLI-SQARWA) algorithm that (a) guarantees zero blocking due to signal degradation and wavelength contention and (b) aims at minimizing the total required number of network components i.e. regenerators and all-optical wavelength converters (AOWCs). Further, in view of reducing the time delay due to optical-electrical-optical (OEO) conversions, we propose a novel electro-optical hybrid translucent node architecture. We show that PLI-SQARWA outperforms a recent heuristic for RWA and regenerator placement (RP) in terms of capital expenditure (CapEx) and time delay; while demonstrating superior blocking performance at all traffic loads. In addition, at high traffic loads, PLI-SQARWA also starts to provision savings on operational expenditure (OpEx). We proceed to the performance comparison of network equipped with the proposed hybrid node and existing translucent and transparent node architectures. The results clearly show that use of the hybrid node incurs less time delay at a similar blocking performance shown by nodes which use OEO conversion for both, regeneration and/or wavelength conversion. The results presented also highlight the significance of equipping the PLI-RWA routing phase with signal quality awareness in order to reduce the network component count and the use of AOWCs to minimize time delay due to OEO conversions.

Novel real-time homodyne coherent receiver using a feed-forward based carrier extraction scheme for phase modulated signals

We report a novel real-time homodyne coherent receiver based on a DPSK optical-electrical-optical (OEO) regenerator used to extract a carrier from carrier-less phase modulated signals based on feed-forward based modulation stripping. The performance of this non-DSP based coherent receiver was evaluated for 10.66 Gbit/s BPSK signals. Self-homodyne coherent detection and homodyne detection with an injection-locked local oscillator laser was demonstrated. The performance was evaluated by measuring the electrical signal-to-noise (SNR) and recording the eye diagrams. Using injection-locking for the LO improves the performance and enables homodyne detection with optical injection-locking to operate with carrier-less BPSK signals without the need for polarization multiplexed pilot-tones.

Joint port-cost and power-consumption savings in hybrid hierarchical optical networks

In optical networks, with the number of wavelengths in fibers increasing, the size and cost of Optical Cross-Connects (OXC) have been increased. Waveband merging technology, which groups several wavelength routes into a single waveband tunnel with at least two hops, could perform port-cost savings by reducing the size and cost of OXC since switching one waveband in the All Optical (OOO) domain only consumes two ports at each bypass node. On the other hand, the absence of wavelength conversion restricts the capability of OOO–OXC. Therefore, designing a hybrid hierarchical node to transmit wavebands in an OOO switch and add/drop local requests or perform wavelength conversion in an Optical-Electrical-Optical (OEO) switch has been one of the promising solutions for next-generation optical networks. However, due to the increasing effects of greenhouse gases and the drastic consumption of power, port-cost and power-consumption savings are becoming the new and twin objectives to further develop hybrid hierarchical optical networks. In this paper, we jointly consider port-cost and power-consumption in a hybrid hierarchical optical network and propose efficient approaches including Integer Linear Programming (ILP) models and heuristics. Simulation results of two heuristic approaches, a Cost and Power savings algorithm based on an End-to-End waveband Merging strategy (CPEEM) as well as a Cost and Power savings algorithm based on a Sub-Path waveband Merging strategy (CPSPM), show that the cost of Transmitting Ports (TPs) used in an OOO switch is in contrast to the use of the power consumed by the OEO part of a hybrid hierarchical node. Moreover, comparing with CPEEM, CPSPM has a better performance for port-cost savings but the performance improvement is at the cost of higher power consumption in an OEO switch. On the contrary, CPEEM has a better performance for power-consumption savings but the performance improvement is achieved at the expense of a higher cost of transmitting ports comparing with CPSPM. Based on the parameter, Boundary of Consumed Power (BCP), a New Integrated Algorithm (NIA) that could effectively choose between CPEEM or CPSPM according to the current network state is proposed to obtain the trade-off performances.

Photonics for Solving Unbundling in Next-Generation WDM-PON

Modern telecommunication networks are quickly evolving from passive content use to an evolutionary and much more participative social model that demands huge capacity, low power consumption, and low cost. Wavelength-division-multiplexing passive optical network (WDM PON) represents one of the current solutions to meet different network requirements. Nevertheless, in order to fully exploit the potential of WDM PON, unbundling issues still require a more efficient management, specially when the network connections get higher, to achieve high flexibility, scalability, minimum hiring together with low power consumption and low cost. Here, unbundling in WDM PON is handled in optical domain in order to exploit the higher bandwidth optics can offer with respect to electronics, avoiding high power consuming due to optical-electrical-optical (OEO) conversions. The use of photonic signal processing enables not only high bit rate but also scalability, easy reconfigurability, modularity, minimum number of fiber links, and “pay as you grow” strategy implementation. An innovative architecture based on WDM/time-division-multiplexing conversion is proposed, and all required all-optical subsystems are experimentally demonstrated, as proof of concept, exploiting nonlinear optical fiber. Power penalty lower than 3 dB is verified for each optical block. Power requirements for each subsystem are also reported. Moreover, the use of new integrated technologies can strongly reduce power consumption footprint and implementations cost.

Switch Port Allocation in WDM Networks with Hybrid Optical-Electronic Switching Nodes

We investigate the problem of switch port allocation in WDM networks that use the hybrid optical-electronic switching node architecture. The objective is to support given traffic demands while minimizing the number of electronic switch ports used, or equivalently minimizing the number of established lightpaths. We first formulate the problem as a mixed integer linear programming (MILP) problem. However, due to the high computational complexity of exact optimization, we develop a simulated annealing (SA) algorithm to get an approximate solution. Results from the SA algorithm demonstrate that, compared to the optical-electrical-optical (O-E-O) node architecture, a WDM network that employs the hybrid switching node architecture requires many fewer lightpaths. We also develop a lightpath assignment heuristic which requires much less computation time than the SA algorithm while maintaining close objective values. The lightpath assignment heuristic is used to investigate the switch port allocation behaviors. Simulation results show that nodes with high degrees or with small average node distances require large numbers of optical switch ports. Moreover, nodes with large amounts of terminate (originated/destined) traffic require large numbers of electronic switch ports. Since the lightpath assignment heuristic requires small computation time, it can be used in the network design process in which a large number of network scenarios must be considered.

A new multi-granularity traffic grooming routing algorithm in IP over WDM networks

In IP over WDM networks, since there is a large bandwidth gap between a wavelength capacity and the actual bandwidth required by each user, it is necessary to multiplex low-rate traffic streams (LRSs) into lightpaths by traffic grooming. However, with the number of wavelengths increases, a large number of all optical (OOO) transmitting ports are consumed. Meanwhile, the multi-hop grooming with incorporating full-wavelength conversion capacity in each node requires too many optical–electrical–optical (OEO) ports inevitably. To solve theses problems, waveband switching and intra-band wavelength conversion are proposed. By integrating traffic grooming and waveband switching, this paper devises a new multi-granularity traffic grooming mechanism with the function of intra-band wavelength conversion. Based on the proposed mechanism and integrated grooming policy (IGP), a new heuristic routing algorithm called multi-granularity traffic grooming based on integrated auxiliary graph (MGIAG) is also proposed since the traffic grooming problem is NP-hard. Simulation results show that, compared to traditional integrated grooming algorithm (IGA), MGIAG can save more ports and obtain lower blocking probability. Compared to traditional single-hop traffic grooming algorithm (SHA), lower blocking probability and more savings in transmitting ports can be achieved by multi-hop grooming in MGIAG and IGA although they consume more OEO ports.

Traffic design to reduce the number of OEO conversions in multi-stage access network

It is important to realize the efficient accommodation of access traffic for various services that will have a wide dynamic range of bandwidth. To achieve this, we are studying a new access network based on multi-stage semiconductor optical amplifiers (SOAs), which has a multi-access point that separately accommodates different services. This paper describes the configuration and advantage of this network and presents a traffic design obtained by simulations that examined the number of optical-electrical-optical (OEO) conversions at first-in first-out (FIFO) controlling packets with a view to reducing power consumption.

Reach Extension Strategies for Passive Optical Networks [Invited

We present here the main results for reach extension in passive optical network (PON) technologies. Both passive and active architectures integrating several multiplexing techniques are studied, and they provide promising results for the future generation of optical access networks. Extender boxes based on optical amplification and optical-electrical-optical (OEO) repeaters are evaluated over a standardized gigabit PON (GPON) system. With this architecture, the optical budget of a class B+ access network can be increased so as to achieve a total budget of 65 dB. Furthermore, using the technique of remotely pumped optical amplification on a wavelength division multiplexing/time division multiplexing (WDM/TDM) topology, the optical budget of a class C+ PON tree could be increased by an additional 22 dB amounting to a total budget of 55 dB. These results are promising since they should enable high flexibility on the optical budget to achieve more reach and splitting ratio, which are prerequisites needed for the migration to the next-generation access networks.

Layer-preference policies in multi-layer GMPLS networks

We address the problem of routing Label Switched Paths (LSPs) in multi-layer networks based on the Generalized MultiProtocol Label Switching (GMPLS) paradigm. In particular, we pursue policies for choosing the appropriate layer to host a new LSP request, as we find that such layer-preference policies have significant impact on network performance. We discuss several simple layer-preference policies and we reveal why these simple policies ruin network performance in the long run. Consequently, we develop an efficient heuristics, the Min-phys-hop routing and wavelength assignment algorithm, to govern the selection of the best layer of a multi-layer network in which to host new LSP requests. We discuss the applicability of this algorithm with respect to the state-of-the-art GMPLS standards, above all, the GMPLS routing extensions to OSPF-TE. By extensive simulations, we justify that the Min-phys-hop algorithm produces close-to-optimal blocking and resource consumption under almost all possible selections of input parameters, and this is regardless of the wavelength and Optical-Electrical-Optical (OEO) conversion capability present in the network.

Path decomposition under a new cost measure with applications to optical network design

We introduce a problem directly inspired by its application to DWDM ( dense wavelength division multiplexing ) network design. We are given a set of demands to be carried over a network. Our goal is to choose a route for each demand and to decompose the network into a collection of edge-disjoint simple paths. These paths are called optical line systems . The cost of routing one unit of demand is the number of line systems with which the demand route overlaps; our design objective is to minimize the total cost over all demands. This cost metric is motivated by the need to minimize O-E-O ( optical-electrical-optical ) conversions in optical transmission. For given line systems, it is easy to find the optimal demand routes. On the other hand, for given demand routes designing the optimal line systems can be NP-hard. We first present a 2-approximation for general network topologies. As optical networks often have low node degrees, we offer an algorithm that finds the optimal solution for the special case in which the node degree is at most 3. Our solution is based on a local greedy approach. If neither demand routes nor line systems are fixed, the situation becomes much harder. Even for a restricted scenario on a 3-regular Hamiltonian network, no efficient algorithm can guarantee a constant approximation better than 2. For general topologies, we offer a simple algorithm with an O (log K )- and an O (log n )-approximation, where K is the number of demands and n the number of nodes. This approximation ratio is almost tight. For rings, a common special topology, we offer a more complex 3/2-approximation algorithm.

G+: Enhanced Traffic Grooming in WDM Mesh Networks using Lighttours

In this article, a new technique for grooming low-speed traffic demands into high-speed optical routes is proposed. This enhancement allows a transparent wavelength-routing switch (WRS) to aggregate traffic en route over existing optical routes without incurring expensive optical-electrical-optical (OEO) conversions. This implies that: a) an optical route may be considered as having more than one ingress node (all inline) and, b) traffic demands can partially use optical routes to reach their destination. The proposed optical routes are named "lighttours" since the traffic originating from different sources can be forwarded together in a single optical route, i.e., as taking a "tour" over different sources towards the same destination. The possibility of creating lighttours is the consequence of a novel WRS architecture proposed in this article, named "enhanced grooming" (G <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> ). The ability to groom more traffic in the middle of a lighttour is achieved with the support of a simple optical device named lambda-monitor (previously introduced in the RingO project). In this article, we present the new WRS architecture and its advantages. To compare the advantages of lighttours with respect to classical lightpaths, an integer linear programming (ILP) model is proposed for the well-known multilayer problem: traffic grooming, routing and wavelength assignment The ILP model may be used for several objectives. However, this article focuses on two objectives: maximizing the network throughput, and minimizing the number of optical-electro-optical conversions used. Experiments show that G <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> can route all the traffic using only half of the total OEO conversions needed by classical grooming. An heuristic is also proposed, aiming at achieving near optimal results in polynomial time