Wavelength Division Multiplexing Networks Research Articles

Horn-Waveguide RSOA-EAM as a Colorless Emitting Source With Reduced Crosstalk

We proposed, designed, and fabricated a monolithically integrated horn-waveguide asymmetric reflective semiconductor optical amplifier electro-absorption modulator (RSOA-EAM) to discriminately process down- and up-stream signals for colorless optical network units in the wavelength-division multiplexing passive optical network (PON). It is demonstrated that the horn-waveguide RSOA-EAM can effectively saturate the downstream signal and linearly amplify the upstream signal, an indispensable feature that is required by the RSOA-EAM to simultaneously erase the downstream signal for a clean seed and to amplify the reloaded upstream signal in its return path. The measurement shows that our fabricated device can reduce the extinction ratio of the 10-Gb/s downstream signal from 5 to 1.2 dB, and a 5-Gb/s upstream signal can be reloaded onto the “clean” carrier, with a clear eye-opening after the linear amplification of its power to over 1 dBm. The measured bandwidth of the device is 25 nm (from 1571 to 1596 nm), far beyond the required 5-nm (from 1575 to 1580 nm) colorless operating range for downstream signals in the 10-Gb/s Ethernet PON and X Gb/s PON.

5 × 10 Gbps WDM-CAP-PON based on frequency comb using OFDM with blue LD

Presently, optical access networks are in great demand to meet the bandwidth requirement due to rapid growth in high speed applications for smart devices, cloud computing, big data analysis and other 5G applications. In this paper, 5 × 10 Gb/s wavelength division multiplexing carrier-less amplitude phase modulation-passive optical network (WDM-CAP-PON) with frequency comb is proposed and demonstrated. Also, 450 nm blue laser diode having bandwidth 0.8 GHz is used for visible light communication using 6 m FSO link to support cost effective high data rate optical network. The WDM-CAP-PON employing orthogonal frequency division multiplexing has been analysed in terms of tolerance to the fiber non-linearities through the effect of variations in launch power (− 5 to 4 dBm), datarate (2.5–40 Gb/s) and distance (20–110 km) on Q-factor and error vector magnitude (EVM%) by considering pre-, post- and symmetrical-dispersion compensation schemes. It is reported that post-compensation is superior to pre- and symmetrical-compensation schemes to achieve the minimum 3.8 × 10−3 BER under 7% forward error correction (FEC). The faithful transmission distance achieved for 10 Gb/s WDM-CAP-PON using post dispersion compensation scheme is 110 km.

Energy- and fatigue-aware RWA in optical backbone networks

Connection provisioning in Wavelength Division Multiplexing (WDM) networks needs to account for a number of crucial parameters. On the one hand, operators need to ensure the connection availability requirements defined in Service Level Agreements (SLAs). This is addressed by selecting an appropriate amount of backup resources and recovery strategies for the connections over which services are provisioned. Services requiring less strict availability requirements can be routed over unprotected lightpaths. Services with more strict availability requirements are provisioned over protected lightpaths in order to cope with possible failures in the network. Another important aspect to consider during the provisioning process is energy efficiency. Green strategies leverage on setting network devices in Sleep Mode (SM) or Active Mode (AM) depending on whether or not they are needed to accommodate traffic. However, frequent power state changes introduce thermal fatigue which in turn has a negative effect on the device lifetime. Finally, in multi-period traffic scenarios, it is also important to minimize the number of reconfigurations of lightpaths already established in the network in order to avoid possible traffic disruptions at higher layers. The work presented in this paper tackles the connection provisioning paradigm in an optical backbone network with a multi-period traffic scenario. More specifically the paper looks into the interplay among (i) energy efficiency, (ii) thermal fatigue, and (iii) lightpath reconfiguration aspects. To this end, the Energy and Fatigue Aware Heuristic with Unnecessary Reconfiguration Avoidance (EFAH-URA) is introduced, showing that it is possible to balance the three aspects mentioned above in an efficient way. When compared to the pure energy-aware strategies, EFAH-URA significantly improves the average connection availability for both unprotected and protected connections. On the other hand, it is done at the expense of reduced energy saving.

Load and Link Aware Protection Switching Technique for WDM Networks

Abstract Providing reliable connection-oriented services in wavelength division multiplexing (WDM) networks becomes challenging because of bad channel quality and overload. Most of the existing works have not considered node failures and congestion which are the essential characteristics for survivable routing. In this paper, a load and link aware protection switching technique for survivable routing in WDM networks is proposed. The technique estimates k-shortest paths for a connection request. Based on four different path possibilities, it provides the best path as connection path in terms of bandwidth. For establishing the primary path, the least virtual hop first routing algorithm is used. If the source node receives either failure or congestion warning message from the intermediate nodes, it triggers the load balanced rerouting algorithm for establishing the backup path. The proposed technique is simulated in NS-2, and the simulation results prove the efficiency of the scheme.

Integrated all-optical wavelength and polarization conversion of orbital angular momentum carrying modes.

Wavelength division multiplexing (WDM) using higher-order spatial modes such as orbital angular momentum (OAM) through a channelized bandwidth provides enhanced capacity communication systems. An all-optical wavelength converter is a key function in implemented WDM networks to overcome the wavelength contentions. In addition, a polarization converter provides efficient control on the state of polarization for encoded data channels in the optical networks. This paper proposes a novel versatile-designed integrated optical device with Ycut ridge lithium niobate photonic wire configuration that acts as a wavelength or polarization converter for data modulated on OAM. It is schemed in such a way that generates decomposed guided modes with a new wavelength and polarization via cascaded second harmonic generation/difference frequency generation (cSHG/DFG) and type-II DFG nonlinear interactions, respectively, where their desired relative phase is achieved by a linear electro-optical effect in the successive phase shifter part. The low loss ≤0.09 dB/cm, high purity (≥94%), and low voltage (≤4 V) of the high-speed proposed modulator enable its compatible operation in commercial wireless and fiber-based polarization-multiplexed WDM communication systems.

Greedy randomized adaptive search procedure for joint optimization of unicast and anycast traffic in spectrally-spatially flexible optical networks

The volume of data traffic in backbone networks is increasing at a speed that exceeds the growth rates of capacities offered in currently used wavelength division multiplexing (WDM) networks. As a short term solution to the potential capacity crunch, the concept of flexible-grid elastic optical networks is nowadays implemented in many backbone networks. However, in a longer term the space division multiplexing (SDM) technology is the most promising solution for satisfying the capacity requirements in future optical networks. The combination of both technologies allows for realization of spectrally-spatially flexible optical networks (SS-FONs). In this paper, we focus on a network scenario in which two different types of traffic flows are carried over an SS-FON, namely, unicast and anycast flows. Unicast flows are used for basic one-to-one communication, while anycast flows — defined as one-to-one-of-many communication — are related to the network traffic generated in data centers and the fact that data centers placed in different network locations can provide the same service or content to network users. For provisioning of lightpaths for both types of traffic, we address the basic optimization problem in SS-FONs, which is routing, space and spectrum allocation (RSSA). The aim of this study is threefold. First, we propose an effective metaheuristic method based on the greedy randomized adaptive search procedure (GRASP) to solve the RSSA problem. Second, we compare performance of the proposed GRASP method against reference optimization approaches. Finally, we present and discuss a wide range of experiments focused on analysis of SS-FONs with joint unicast and anycast traffic. The main conclusions are: (i) the proposed GRASP algorithm provides results very close to optimal (only 0.5% optimality gap) for smaller problem instances and significantly outperforms other heuristics for larger problem instances (in average around 6.8% better than the reference simulated annealing algorithm); (ii) the use of anycast connections in SS-FONs allows to improve the network performance in terms of spectrum usage.

A novel WDM-MAN enabling cross-regional reconfiguration and comprehensive protection based on tangent-ring

Abstract A reconfigurable and reliable wavelength division multiplexing (WDM) metro-access optical network architecture is proposed in this paper. With the establishment of one optical transmitter in the optical network unit (ONU) and the reuse of optical distribution network, three kinds of reconfigurable WDM optical networks can be successfully built to achieve efficient inter and intra PON communication in the physical layer. With the adoption of multiple topologies based on single ring, four-level protections of feeder and distribution fibers can be achieved. With the creative design of flexible distribution node (FDN), the transmission wavelengths in the central office can be not only transmitted to the express ONUs connected straight with FDN, but also routed to the indirect ONUs hung in the remote node. Finally, large capacity, high reliability, low cost and great transmission performances at 10 Gbps and 2.5 Gbps data rate are obtained via analyses and simulation

Blocking Probability Analysis for Optical Banyan Networks With Link Failure

Highly fault-tolerant optical switch is becoming a critical network element for large wavelength division multiplexing mesh networks. Optical nodes built on replicated banyan network (RBN) structures are attractive for serving as optical switching systems due to the nice properties of banyan network structures. Furthermore it is expected that an optical RBN structure also has a good fault-tolerant capability because it consists of multiple identical banyan networks. Previous analytical models have been developed to understand the blocking behaviors of optical RBN networks without taking into account the link failure in optical RBN networks. In this paper, we conduct the link failure-tolerant analysis of optical RBN networks and present an analytical model for the blocking probability of optical RBN networks when link failures are taken into account. The model is significant because it provides network developers a quantitative guidance to determine the effects of network failure on the overall blocking behaviors of optical RBN networks and enables a desirable tradeoff to be made between blocking probability and hardware cost in a faulty optical RBN network.

Realizing Exchanged Crossed Cube Communication Patterns on Linear Array WDM Optical Networks

The exchanged crossed cube, denoted by [Formula: see text], is a novel interconnection network with fewer edges and smaller diameter compared to other variations of the corresponding hypercube. The linear array, denoted by [Formula: see text], is one of the most popular topologies in optical networks. This paper addresses the routing and wavelength assignment for realizing [Formula: see text] communication pattern on wavelength division multiplexing (WDM) optical network [Formula: see text], where [Formula: see text]. We prove that the congestion for [Formula: see text] on [Formula: see text] is equal to [Formula: see text], which is the lower bound of the minimum number of required wavelengths. In addition, an embedding scheme and an optimal wavelength assignment algorithm that achieve this bound are also proposed.

AWG-based WDM ring networks: High-performance and low-cost system designs

Optical packet switching (OPS) ring networks are regarded as being promising solutions for future optical metropolitan area networks. In this paper, we propose novel arrayed-waveguide grating (AWG)-based wavelength division multiplexing (WDM) ring network systems that are aimed at achieving low-cost, scalable, and high-performance systems. By exploiting the cyclic routing properties and spatial wavelength reuse of a passive 2*2 AWG device, we redesign the ring network into a two-subring network, connected through the AWG device. The network is governed by a novel distributed medium access control (MAC) scheme, and we further derive a highly efficient and fair bandwidth allocation in accordance with a quota. A previously proposed experimental optical packet-switched WDM metro-ring network, called HOPSMAN, has shown to have exceptional performance among the OPS ring network studies. We show simulation and analytic results to demonstrate that our proposed system have achieved enhanced performance of the TT (tunable transmitter)-TR (tunable receiver)-based HOPSMAN by 1.5 times but have used only low-cost TT-FR (fixed-tuned receiver) or FT (fixed-tuned transmitter)-FR optical devices. Thus, the proposed networks achieve exceptional network throughput and also greatly reduce system costs.

Performance investigation of MLR optical WDM network based on ITU-T conforming fibers in the presence of SRS, XPM and FWM

This article investigates the performance degradation of a mixed line rate (MLR) optical wavelength division multiplexing network in the presence of the combined FWM, XPM and SRS effects. For performance evaluation a novel mathematical model is developed which evaluates the results in terms of quality-factor. Further, the simulations are performed (i) based on the optical frequency grid defined by the ITU-T Recommendation G.692, and (ii) considering the ITU-T compliant optical fibers viz., G.652, G. 652D, G. 653, G. 654, G.655, and LEAF. The obtained results show that among the various considered fibers and modulation format configuration cases, irrespective of spacing between the channels (i) SMF (G.652) and DSF (G.653) fibers provide the best and the worst performances, respectively, and (ii) a combination of the central channel transmitting at 40 Gbps using the duo-binary modulation format with adjacent channels transmitting at 10 Gbps using OOK modulation format, provides the best performance. However, with increase in spacing between the channels, the performance is enhanced owing to mitigation of the deleterious non-linear effects. Overall, the results clearly show that choice of the data rate of both, the central channel and its adjacent channel has a major effect on the MLR network performance.

A Capacity Allocation Algorithm for Optical Virtual Private Networks

As the development of optical communication technologies such as Wavelength-Division Multiplexing (WDM), it is important to support virtual private networks (VPN) over WDM networks. In order to overcome the limits of WDM network capacity and achieving more revenue new VPNs, an optimal model supporting both optical VPN and IP VPN on WDM networks is proposed to admit the maximum number of new VPNs without influencing the QoS guarantee for the existing VPNs. Furthermore, three heuristic algorithms are designed to simplify the computation process of getting optimal solution. The simulation results over MESH WDM networks show the algorithm can takes advantage of the reliable transmission capability of WDM networks and provides diverse QoS for different traffic streams by different quality of optical transmission.

Hybrid OFDM RoF-Based WDM-PON/MMW Backhaul Architecture For Heterogeneous Wireless Networks

In this paper, a hybrid backhaul architecture, which is based on wavelength-division multiplexing passive optical networks (WDM-PON) and millimeter-wave (MMW) communications, is proposed to deliver orthogonal frequency-division multiplexing (OFDM) signals in heterogeneous wireless networks. MMW radio-over-fiber (RoF) technique, which combines the advantages of the both optical fiber and wireless communications, is used to simplify the base stations and provide flexibility long reach and high capacity connections. The feasibility of the proposed hybrid backhaul architecture is investigated via the bit-error rate (BER) performance of a downlink under the impacts of fiber nonlinear, wireless fading and noise components including clipping noise, amplifier noise and photodetector noise. The numerical results obtained from this study help to determine the optimum system parameters such as the optical launched power, modulation index, and amplifier gain so as to minimize the link’s BER.

Incorporating grooming in protection based elastic optical network

The transition from wavelength routed optical networks to the elastic optical network was evident because of the limitations of the wavelength division multiplexing (or WDM) optical networks. The elastic optical network is superior to the WDM optical networks because of its flexible spectral allocation and finer grid granularity. Since all the optical networks consists of a set of optical fibers which are vulnerable to fiber cut or failure, there should be some mechanism to protect the networks from failure. In this paper, a segment based protection scheme is integrated with a traffic grooming policy that could optimize the network resources as well as provide protection to the network optical fibers. The comparative study of the proposed grooming and protection based approach with a non grooming segment based approach reveal that the grooming based approach has better spectrum utilization and also it is computed in less CPU time than non grooming approach for static multicast traffic demands.

Twin-Ring Optical WDM-MAN Enabling Triple-Hierarchical Reconfigurations and Quadruple-Shared Protections

ABSTRACTAn optical wavelength division multiplexing metro access network is proposed in this paper. With the design of flexible distribution node (FDN), three kinds of reconfigurable networks can be flexibly built to achieve intra- and inter-optical network unit (ONU)-direct communications. With the adoption of multiple tangent twin-ring topologies, four-level shared protections covering both feeder and distribution fibers are also supported. Moreover, the network can be smoothly expanded by adding express ONUs connected to FDNs. Thus, the network can not only achieve capacity increasing but also support full-duplex reconfigurable communication. A reconfigurable transmission algorithm is also set to avoid wavelengths conflict.

Recognition of the optical packet header for two channels utilizing the parallel reservoir computing based on a semiconductor ring laser

In this paper, an all-optical parallel reservoir computing (RC) system with two channels for the optical packet header recognition is proposed and simulated, which is based on a semiconductor ring laser (SRL) with the characteristic of bidirectional light paths. The parallel optical loops are built through the cross-feedback of the bidirectional light paths where every optical loop can independently recognize each injected optical packet header. Two input signals are mapped and recognized simultaneously by training all-optical parallel reservoir, which is attributed to the nonlinear states in the laser. The recognition of optical packet headers for two channels from 4 bits to 32 bits is implemented through the simulation optimizing system parameters and therefore, the optimal recognition error ratio is 0. Since this structure can combine with the wavelength division multiplexing (WDM) optical packet switching network, the wavelength of each channel of optical packet headers for recognition can be different, and a better recognition result can be obtained.

Time-Scheduled Quantum Key Distribution (QKD) Over WDM Networks

Quantum key distribution (QKD) networking over wavelength-division multiplexing (WDM) network infrastructure provides a new paradigm for secure communications across the networks. With limited wavelength resources in existing WDM networks, how to efficiently schedule QKD to provision sufficient secret keys over WDM networks becomes a new challenge. This study proposes a new time-scheduled scheme in combination with quantum key pool (QKP) technique to overcome this challenge. A new architecture of QKD-over-WDM networks is presented, in which QKPs are constructed to decouple secret-key resources from the underlying infrastructure for timely secret-key provisioning. In the time-scheduled scheme, routing, wavelength, and time-slot allocation (RWTA) problem is proposed for efficient QKP construction (QKPC) over WDM networks, in which three sub-problems (i.e., secret-key consumption, time-slot allocation, and time-slot continuity) are discussed, respectively. An integer linear programming (ILP) model and a novel joint path-and-link-based RWTA (JPL-RWTA) heuristic algorithm are designed to solve the RWTA problem, in which the three sub-problems are addressed together. Simulation results indicate that the ILP model and JPL-RWTA algorithm are effective approaches to obtain the positive balance between resource utilization of QKPC and successful probability of QKPC (SPQKPC). Moreover, the SPQKPC can be increased at the cost of reducing the flexibility of secret-key consumption, the uniformity of time-slot allocation, and the proportion of time-slot continuous QKPC to time-slot discrete QKPC requests.

Energy-Saving in IP Over WDM Networks by Putting Protection Router Cards to Sleep

Energy saving is of great interest in current information and communications technology applications. In this paper, we consider energy saving for an IP over wavelength division multiplexed (WDM) optical network by putting protection router cards to sleep when the network is operating normally. Doing this requires that we must jointly consider several aspects. These are multi-layer traffic grooming, network protection, and the assignment of router ports/cards for working and protection optical channels. By employing different network protection techniques and the multi-hop traffic grooming strategy, we develop mixed integer linear programming (MILP) models for the optimization problem by considering five different router port assignment schemes. These aim to minimize the total power consumption of the whole network. Subsequently, to tackle the computational difficulty of the MILP models, we propose an efficient heuristic algorithm to handle large networks. This heuristic algorithm consists of two steps, i.e., survivable traffic grooming and router port assignment. Results show that the proposed energy-saving strategy is efficient and can significantly reduce the total power consumption of an IP over WDM network, where the assignment strategy for router cards is of primary importance for energy-saving efficiency. We also observe that the proposed heuristic algorithm performs almost as well as the MILP models in terms of the energy efficiency of the system.

1.25–2.5 Gb/s Simple Nyquist Transmitters for Coherent UDWDM-PON with Enhanced Spectral Efficiency

ABSTRACTWe present a coherent ultra-dense wavelength division multiplexing passive optical network (UDWDM-PON) with enhanced spectral efficiency. The benefit of using Gaussian or Nyquist pulse-shaping filters at the transmitter is evaluated through numerical simulations and experiments. The transmitters consist of directly phase modulated distributed feedback (DFB) lasers through beat signals whose duty-cycle and amplitude are digitally adjusted. The results show that transmitting a Nyquist-shaped signal achieves a 25% spectral saving allowing to place 2.5 Gb/s/user data in 6.25 GHz channels. Furthermore, the proposed transmitter tolerates differential link-losses of 15 dB at Rx sensitivity of ‒44 dBm at BER=10‒3 with intradyne detection.

Reverse Bias Voltage Controlled Burst-Mode Booster SOA in λ-Tunable ONU Transmitter for High-Split-Number TWDM-PON

This paper presents a λ-tunable optical network unit (ONU) burst-mode transmitter (B-Tx) with high output power and low burst-off-level power for high-splitnumber time and wavelength division multiplexing passive optical networks (TWDM-PONs). The proposed ONU B-Tx utilizes a burst-mode booster semiconductor optical amplifier (SOA) with a control technique for reverse bias voltage that creates an optical power absorption effect in the burstoff- level state. This paper introduces the design of the biasvoltage- state control circuit, simulations of control-circuit operation, evaluations of the static optical power-absorption effect, and burst-mode operation performance in the booster SOA operated by reverse bias voltage. High output power of over +7.4 dBm and low burst-off-level power of under −73.4 dBm∕15 GHz are successfully achieved in all upstream channels. Crosstalk penalty measurements confirm a very low penalty of under 0.1 dB, which leads to a 256 splitnumber TWDM-PON.