Wavelength Division Multiplexing Networks Research Articles

Designing, Operating, and Reoptimizing Elastic Optical Networks

Emerging services and applications demanding high bitrate and stringent quality of service requirements are pushing telecom operators to upgrade their core networks based on wavelength-division multiplexing (WDM) to a more flexible technology for the more dynamic and variable traffic that is expected to be conveyed. Finally, academy- and industry-driven research on elastic optical networks (EON) has turned out into a mature enough technology ready to gradually upgrade WDM-based networks. Among others, key EON features include flexible spectrum allocation, connections beyond 100 Gb/s, advanced modulation formats, and elasticity against time-varying traffic. As a consequence of the variety of features involved, network design and algorithms for EONs are remarkably more complex than those for WDM networks. However, new opportunities for network operators to reduce costs arise by exploiting those features; in fact, the classical network life cycle based on fixed periodical planning cycles needs to be adapted to greatly reduce overprovisioning by applying reoptimization techniques to reconfigure the network while it is in operation and to efficiently manage new services, such as datacenter interconnection that will require provisioning multicast connections and elastic spectrum allocation for time-varying traffic. This paper reviews and extends mathematical models and algorithms to solve optimization problems related to the design, operation, and reoptimization of EONs. In addition, two use cases are presented as illustrative examples on how the network life cycle needs to be extended with in-operation planning and data analytics thus adding cognition to the network.

Multipath Routing and Wavelength Assignment Technique in Optical WDM Mesh Networks

AbstractA routing and wavelength assignment (RWA) technique for supporting multipath traffic in optical wavelength-division multiplexing (WDM) mesh network is proposed in this paper. The network can be preceded by accomplishing two processes: one is establishing connection node and the second one is identifying the multipath and assigning wavelength. The connection node is selected based on the load and current traffic-carrying capacity of that node. During wavelength allocation mechanism, cost function is considered as the major criterion. Based on the cost involved in every path, the wavelengths are selected such that wavelength with the minimum cost is allocated to that particular path. This technique efficiently allocates the wavelength to the selected multiple paths and the traffic is routed to the destination using multiple paths with wavelength allocation. For simulation, NS2 simulator is used by applying the optical WDM network simulator patch. The proposed multipath RWA technique is compared with the existing RWA technique. We achieved a throughput of 12,625 packets for ten numbers of wavelengths. But the existing approach achieved a throughput of 10,189 packets only for the same numbers of wavelengths. Channel utilization is more, and delay is less compared with the existing technique. Hence, the proposed method is very efficient, since the router effectively routes the traffic within the network.

Full monitoring for long-reach TWDM passive optical networks.

This paper presents a novel and simple fiber monitoring system based on multi-wavelength transmission-reflection analysis for long-reach time and wavelength division multiplexing passive optical networks. For the first time, the full localization functionality of long-reach passive optical networks is possible with the proposed monitoring scheme, including supporting fault detection, identification, and localization in both feeder and distribution fiber segments. By measuring the transmitted and reflected/backscattered optical powers launched by an unmodulated continuous-wave optical source, the proposed solution is able to supervise the network with good spatial accuracy, a high detection speed and a low impact on data traffic. Both the theoretical analysis and experimental validation show that the proposed scheme is capable of providing an accurate fault monitoring functionality for long-reach time and wavelength division multiplexing passive optical networks.

Long reach DWDM-PON with 12.5 GHz channel spacing based on comb source seeding

A long reach dense wavelength division multiplexing passive optical network (DWDM-PON) with 12.5 GHz channel spacing is proposed and experimentally demonstrated. An optical frequency comb source is used to provide the multiwavelength seeding light, while reflective semiconductor optical amplifiers (RSOAs) are installed in both optical line terminal (OLT) and optical network units (ONUs) as colorless transmitter. The experimental results show that the bidirectional transmission for 1.2 Gbit/s data rate is achieved over 80 km single mode fiber (SMF).

A traffic-depended multi-buffer node architecture and an effective access technique under symmetric and asymmetric IP traffic scenarios for unslotted ring WDM MANs

Abstract This study aims to put forward an extensive discussion about the increasing demand for available bandwidth to serve the multiple types of traffic in modern wavelength division multiplexing (WDM) metropolitan area networks (MANs). A traffic-depended multi-buffer node architecture in conjunction with an efficient asynchronous transmission WDM access (WDMA) protocol to serve the variable size Internet packets in ring MANs is proposed. The structure of the multi-buffer node architecture is determined by the probability distribution of each packet size category in the MAN traffic, providing storage and dropping events equity among the nodes. The adopted WDMA algorithm satisfies the requirement for high performance efficiency especially under high offered load, by taking care to optimally face the bandwidth fragmentation problem and to maximize the bandwidth exploitation, while it effectively avoids both the packets collisions over the wavelengths and the destination conflicts. Numerical results prove that the proposed network model achieves throughput improvement up to 334% as compared with the relative study of Pranggono and Elmirghani (2011). An analytical framework is developed for the protocol throughput predictions under both symmetric and asymmetric IP traffic scenarios. Also, the proposed protocol performance is thoroughly investigated through simulation results based on Poisson and self-similar traffic model statistics, for both traffic scenarios.

Fault Tolerance in Passive Optical Networks: A Survey

Passive optical networks play an important role in fiber access system in the world today. Time division multiplexing-passive optical network is a fast emerging architecture that uses only passive components. In wavelength division multiplexing, passive optical network each light path can carry a huge amount of traffic failure may damage the end user applications. Hence fault tolerance has an important issue on this network. In a survey Studies many architectures, protocols and techniques to remove or overcome failures in the access network. Also in this survey study, methods for recovering from channel failures, link failures and node failures. In this paper we discussed the performance of the survey. Survivability is a critical issue in a wavelength division multiplexing optical networks.

Using maximum spectrum of continuous wavelet transform for demodulation of an overlapped spectrum in a fiber Bragg grating sensor network

The maximum spectrum of the continuous wavelet transform (MSCWT) is proposed to demodulate the central wavelengths for the overlapped spectrum in a serial fiber Bragg grating (FBG) sensing system. We describe the operation principle of the MSCWT method. Moreover, the influence of the interval gap between two FBG wavelengths, 3 dB bandwidths, and optical powers of the reflected spectra are discussed. The simulation and experimental results indicate that the MSCWT can resolve an overlapped spectrum and decode the central wavelength with high accuracy. More importantly, the proposed peak detection method can enhance the sensing capacity of a wavelength division multiplexing FBG sensor network.

Cost-effective coherent ONU transceiver based on single directly modulated laser.

A cost-effective structure is proposed for the optical network unit (ONU) transceivers in coherent ultra-dense wavelength division multiplexing passive optical network (UDWDM-PON), which is based on a single directly modulated laser (DML). This is the first time that a DML is used as both optical transmitter in upstream and local oscillator (LO) for coherent detection in downstream. The impact of extinction ratio (ER) of signal from DML is investigated and optimized by adapting the driving amplitude and bias of DML. Each UDWDM grid accommodates a pair of bi-directional signal, where heterodyne detection is used due to the Rayleigh backscattering (RB) from the bi-directional transmission. The impact of frequency offset (FO) between upstream and downstream signal is also investigated. Finally, 2.5-Gb/s bi-directional transmission of OOK signal over 60-km SSMF is experimentally demonstrated within the 12.5-GHz grid, achieving about -43 and -45.5 dBm receiver sensitivity in the downstream and upstream, respectively.

A High Spectral Efficiency Coherent RoF System Based on OSSB Modulation With Low-Cost Free-Running Laser Sources for UDWDM-PONs

A coherent radio over fiber (RoF) system based on optical single-sideband modulation with no optical carrier (OSSB) for ultradense wavelength division multiplexing passive optical networks (UDWDM-PONs) is proposed and experimentally demonstrated. For one channel of the UDWDM-PONs, at the transmitter, the OSSB RoF signal is generated using a dual parallel Mach–Zehnder modulator (DP-MZM) with a real-valued precoded microwave vector signal which is applied to the DP-MZM via the two electrodes with one having a 90° phase shift. Then, the OSSB RoF signal is sent to a coherent receiver over a single-mode fiber (SMF). The coherent receiver with a free-running laser source as a local oscillator (LO) is used to perform the coherent detection. To recover the standard microwave vector signals from the real-valued precoded microwave vector signal that is embedded in a strong phase noise introduced by both the transmitter laser source and the LO laser source, a digital signal processing algorithm is developed to perform phase noise cancellation. An experiment is performed. The transmission of a 1.25-Gbps quadrature phase shift keying, a 1.875-Gbps eight-phase shift keying (8-PSK), and a 2.5-Gbps 16 quadrature amplitude modulation (16-QAM) microwave vector signals with a channel spacing as narrow as 3 GHz over a 25-km SMF is experimentally demonstrated. For the transmission of the 2.5-Gbps 16-QAM microwave vector signal, the received optical sensitivity at forward error correction level over a 25-km SMF link is −24.8 dBm, while for the 1.875-Gbps 8-PSK microwave vector signal, it can reach −29.8 dBm which leaves an enough margin to accommodate the splitting losses in the optical distribution networks.

Photon statistics of pulse-pumped four-wave mixing in fiber with weak signal injection**Project supported by the National Natural Science Foundation of China (Grant No. 11527808), the State Key Development Program for Basic Research of China (Grant No. 2014CB340103), the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20120032110055), the Natural Science Foundation of Tianjin, China

We study the photon statistics of pulse-pumped four-wave mixing in fibers with weak coherent signal injection by measuring the intensity correlation functions of individual signal and idler fields. The experimental results show that the intensity correlation function of individual signal (idler) field decreases with the intensity of signal injection. After applying narrow band filter in signal (idler) band, the value of decreases from 1.9 ± 0.02 (1.9 ± 0.02) to 1.03 ± 0.02 (1.05 ± 0.02) when the intensity of signal injection varies from 0 to 120 photons/pulse. The results indicate that the photon statistics changes from Bose–Einstein distribution to Poisson distribution. We calculate the intensity correlation functions by using the multi-mode theory of four-wave mixing in fibers. The theoretical curves well fit the experimental results. Our investigation will be useful for mitigating the crosstalk between quantum and classical channels in a dense wavelength division multiplexing network.

Resource Allocation Optimization for Time and Wavelength Division Multiplexing Passive Optical Network Enabled Mobile Fronthaul With Bitrate-Variable Compressed Common Public Radio Interface

Recently, a cloud radio access network (C-RAN) has been proposed as a candidate architecture for fifth-generation mobile communication. Fronthaul is a new segment in C-RAN. In this paper, we investigate the algorithms for resource allocation in time and wavelength division multiplexing passive optical network enabled front-haul. We formulate an integer nonlinear programming (INLP) model, considering the operation mode of the small cell. A heuristic method is also proposed based on an adaptive parallel genetic algorithm (GA). Three optimization objectives are considered when we implement the resource allocation schemes in the fronthaul: 1) minimize the total number of used wavelengths, 2) minimize the load imbalance of the fronthaul, and 3) minimize the amount of traffic influenced by fronthaul virtual topology change. The results show that INLP and adaptive parallel GA have good performance for resource allocation in the fronthaul. Wavelength resources can be significantly saved in different load scenarios, so that the load difference can be minimized with minimal topology adjustment. Furthermore, the adaptive parallel GA obtains more efficient resource allocation than the traditional GA with much less running time, which makes it applicable for the large-scale fronthaul network optimization with fast convergence.

WDM–CAP–PON integration with VLLC system based on optical frequency comb

In this paper, a wavelength division multiplexing carrier-less amplitude phase modulation passive optical network (WDM–CAP–PON) integration with visible laser light communication (VLLC) system is proposed and experimentally demonstrated. To reduce the cost of WDM system, the optical frequency comb scheme using one Mach–Zehnder modulator (MZM) is utilized and five flat optical combs can be generated. Meanwhile, a blue laser diode (LD) as a VLLC optical source can provide high data rate and long transmission distance. Utilizing overlap frequency domain equalization (OFDE) and negative chirp of MZM, the system performance in both Q-factor and receiver sensitivity can be improved. After 20km standard single mode fiber (SSMF) and 4.5m free space transmission, the experimental results show that 10Gb/s CAP signal can be achieved under 7% forward error correction (FEC) limit of 3.8×10−3.

Symmetric 10 Gb/s wavelength reused bidirectional RSOA based WDM-PON with DPSK modulated downstream and OFDM modulated upstream signals

A 10Gb/s bidirectional wavelength division multiplexing passive optical network (WDM-PON) with reflective semiconductor optical amplifier (RSOA) based colorless optical network unit (ONU) is proposed and analyzed for next generation gigabit class optical access network. Differential phase shift keying (DPSK) modulated signal is used in downstream and further reused as a seeding wavelength for upstream data modulation. By exploiting the constant envelope property of DPSK seed signal, the re-modulation noise in upstream receiver is effectively minimized without employing any constraint on extinction ratio of downstream signal. Orthogonal frequency division multiplexing (OFDM) signal is used in upstream transmission to overcome the limited bandwidth (∼1GHz) response of RSOA remodulation. The results show that the proposed 10Gb/s symmetric WDM-PON can achieve good performance over 25km fiber transmission with error free operation in downstream and bit error rate (BER) lower than forward error correction (FEC) limit in upstream.

Theoretical Investigation of Optical WDM Network Performance in the Presence of FWM and ASE Noise

AbstractIn this article, for an optical star wavelength division multiplexing (WDM) network, with quality factor (

Interfacial Roughness and Temperature Dependence of Narrow Band Thin Film Filters for the DWDM Passive Optical Networks

In the design of new components for passive optical networks (PONs), the non-ideal properties are worth considering. In this paper the influence of interface roughness and temperature changes on final transmittance of downstream channels blocking filters for next generation dense wavelength division multiplexing passive optical networks(DWDM-PONs) is shown. The transmittance as the filter transfer characteristicswas calculated with the transfer matrix method. The roughness was expressed by root mean square deviations from an ideally smooth surface and was taken into account in the modified Fresnel coefficients. It is demonstrated how the interfacial roughness may increase the insertion loss and decrease the channel bandwidth which results in reduction of transmitted light energy through the filter.

Spectral and power efficiency investigation in single- and multi-line-rate optical wavelength division multiplexed (WDM) networks

In order to tackle the increasing heterogeneous global Internet traffic, mixed-line-rate (MLR) optical wavelength division multiplexed (WDM) networks have emerged as the cost- and power-efficient solution. In MLR WDM networks, channels are structured as sub-bands, each of which consists of wavelengths operating at a similar data rate. By reducing the (1) spacing within a sub-band, or (2) spacing between sub-bands operating at different data rates, spectral efficiency can be improved. However, owing to high physical layer impairment levels, decrease in sub-band spacing adversely affects transmission reach of the channels, which results in higher power consumption due to requirement of increased signal regeneration. In this work, we compare power efficiency of various MLR and single-line-rate (SLR) solutions, and also investigate the trade-off that exists between spectral and power efficiency in a WDM network. Simulation results indicate that (1) for high transmission capacities, a combination of 100 Gbps transponders and 40 Gbps regenerators will obtain the highest power efficiency; (2) for long connection distances, a point ofmerging occurs for various SLR and MLR designs, where power consumption is independent of the frequency band distribution; and (3) for MLR systems, both spectral and power efficiency can be improved by using either shorter links with higher bandwidth assignment to 100 Gbps wavelengths, or longer links with higher bandwidth assignment to 40 Gbps wavelengths. Finally, the results indicate that focusing on spectral efficiency alone results in extra power consumption, since high quality of transmission and spectral efficiency leads to increased regeneration.

Model-hierarchical column generation and heuristic for the routing and wavelength assignment problem

The routing and wavelength assignment (RWA) problem typically occurs in wavelength division multiplexing optical networks. Given a number of available wavelengths, we consider here the problem of maximising the number of accepted connections with respect to the clash and continuity constraints. We first propose a new strategy which combines two existing models. This leads to an improved column generation scheme. We also present two heuristics to compute feasible solutions: a hybrid heuristic and the integer solution at the root node of the column generation. Our approaches are compared with the best existing results on a set of classic RWA instances.

Estimation Uncertainties in the Optical Signal-to-Noise Ratio Network Optimization

In this work, we investigate the effects of estimation uncertainties in the optimization of the optical signal-to-noise ratio (OSNR) at the wavelength division multiplexing (WDM) optical networks. The OSNR optimization increases the network throughput and energy efficiency and it enables to minimize the number of retransmissions by higher layers. The OSNR optimization algorithms are related to the optical channel estimation performed by the combinations of optical performance monitors (OPM) measurements, analytical models and numerical simulations. Furthermore, the estimation uncertainties are introduced by several factors such as the availability of monitoring information, monitoring accuracy, imperfection of physical layer and dynamic of channel allocation. Our numerical results have demonstrated the relation between the uncertainties in the channel error estimation, normalized mean squared error (NMSE) and power penalty. The developed methodology can be utilized to determinate the maxim level of acceptable uncertainties in the channel error estimation according the power penalty permitted in the OSNR optimization.

A Multilayer Approach for Optical Network Planning

With the increase in demand to Backbone networks, one became fundamental the application of new telecommunication technologies for efficient use of devices and optical links, such as xPSK modulations with dual polarization, dispersion compensating fibers, coherent detection and digital processing signals. Thus, network planning using analytical models have been proposed in the last years for this purpose. In this paper we propose the use of numerical simulations in wavelength-division multiplexing networks planning via a novel iterative method with high-performance processing, which does an analysis of the quality of transmission in transparent networks.

Chromatic Dispersion Monitoring by Synchronizing the Two Sidebands of the Received Optical Signal

In this paper, a new chromatic dispersion (CD) monitoring technique is proposed in optical fiber networks. It is based on detecting the relative group delay between the upper and lower sidebands of the monitored signal (induced by CD) by shifting the two sideband signals a number of times and at every time they are converted to the same frequency, and then they are coupled together with a phase difference of (180o) and the resulting signal power is measured. In one of the shift stages, it obtains minimum power when the time shift equals the relative group delay (i.e. the two sideband signals are synchronized). Therefore, the relative group delay can be detected through searching the minimum output power and the corresponding time shift. The proposed technique is characterized, compared with other monitoring techniques, by good monitoring range with the ability to determine chromatic dispersion sign, high measurement resolution, fixed sensitivity over the whole measurement range, no modification of the transmitter, not affected by polarization mode dispersion (PMD), good tolerance to the amplified spontaneous emission (ASE) noise and the potential to monitor several channels in wavelength division multiplexing (WDM) networks.