Wavelength Division Multiplexing Networks Research Articles

Plasmonic Filter and Demultiplexer Based on Square Ring Resonator

A ring resonator is a basic component of traditional photonic integrated circuits (PIC), which has been, however, found difficult to be applied efficiently in high-compact plasmonic metal-insulator-metal (MIM) systems. Here, based on a plasmonic band-stop filter with a square ring resonator (SRR), a novel side-coupling method is introduced both numerically and theoretically to achieve a drop in the resonant wavelength in the SRR with considerable efficiency. By introducing the reflector structure, the performance can be appreciably improved. Besides, this structure also has potential for sensing and switching. Finally, a dual demultiplexer based on SRRs is realized at telecommunication wavelengths with comparable performance, which makes it possible to apply ring resonators in on-chip plasmonic wavelength division multiplex (WDM) networks. This work is valuable for PIC design, and will promote the on-chip plasmonic system progress.

Routing and wavelength assignment for exchanged crossed cubes on ring-topology optical networks

The exchanged crossed cube, denoted by $$\textit{ECQ}(s, t)$$ , is a novel graph with fewer edges and smaller diameter compared to other variations of the corresponding hypercube. The ring topology, denoted by $$R_n$$ , is one of the most popular topologies in Wavelength division multiplexing optical networks. This paper addresses the routing and wavelength assignment problem for realizing $$\textit{ECQ}(s, t)$$ communication pattern on $$R_n$$ , where $$n=s+t+1$$ . We propose an embedding scheme. Base on the embedding scheme, a wavelength assignment algorithm using $$2^{s+t-2}+\lfloor 2^t/3\rfloor $$ wavelengths is devised. We show that the wavelength assignment algorithm uses no more than 1.25 times of wavelengths compared to the optimal wavelength number, i.e., it is a factor 1.25 approximation algorithm. Moreover, the number of additional required wavelengths is no more than $$\lfloor 2^{t-1}/3\rfloor $$ .

Fiber-based simultaneous mode and wavelength demultiplexer.

We theoretically design and analyze the performance of a fiber-based linearly polarized (LP) mode demultiplexer using a Fabry-Perot interferometer. The all-fiber geometry of the reported demultiplexer is obtained by writing fiber Bragg gratings (FBGs) in a few-mode fiber (FMF), such that the FBGs act as partial reflecting mirrors for the LP modes. We also demonstrate the ability to decompose a received optical signal into its individual LP components in wavelength-division multiplexing networks.

15-dB Differential Link-Loss UDWDM-PON With Direct Beat Phase Modulated DFBs

A 15 dB differential link-loss ultra-dense wavelength division multiplexing passive optical network (UDWDM-PON) with two optical network units (ONU) spectrally spaced 6.25 GHz is experimentally implemented and tested. The ONU transmitters consist of direct phase modulated distributed feedback lasers through a digital beat signal, whose amplitude and duty cycle are optimized for maximum phase variations, avoiding the need for an analogue equalizer. We achieved receiver sensitivities of −53, −50.5, and −45 dBm for bit rates of 1.25, 2.5, and 5 Gb/s, respectively, at BER $= 4~\cdot ~10^{-3}$ with an intradyne coherent receiver.

Design of a Hybrid Optical amplifier for 64 DWDM Channels network by using EDFA and Raman Amplifier

In this paper a hybrid amplifier EDFA-RAMAN DWDM transmission system is proposed and demonstrated. A new hybrid two-stage optical fiber amplifier for dense wavelength division multiplexing (DWDM) network is observed. The hybrid amplifier is cascaded erbium- doped fiber amplifiers (EDFA) & Raman amplifier which provide a nearly flat gain over 80 nm. The hybrid amplifier has been modeled using an Optic-System version 14 on a DWDM transmission. In this paper we compare Q-factor at different input power i.e. at 0db and at 10 db. Here two different types of apodized function (Uniform & Gaussian) are selected as fiber Bragg grating parameters and system performance is analyzed. Performance of the system is analyzed by using BER analyzer.

Power reduction strategies with differentiated quality of protection in IP-over-WDM networks

This work considers two important aspects of modern communication networks, network survivability, and energy efficiency. Survivability is a design requirement to provide failure recovery against network outages such as fiber cuts. To ensure survivability, traditionally, spare network (i.e., backup) resources are reserved in case of failures of primary (i.e., working) network resources. On the other hand, energy efficiency is required to cope with the continuous growth of the Internet traffic. Backup resources increase the energy consumption, especially if constantly powered-on. Hence, a trade-off between energy efficiency and network resiliency arises. To increase transport capacity and reduce energy consumption, wavelength division multiplexed (WDM) networks are adopted as the most practical solution for data transport in core networks, which are the focus of our work. In WDM networks, different levels of protection (i.e., dedicated, shared) can be implemented for different traffic demands, and different protection levels are characterized by different power consumptions. We consider a differentiated quality of protection (Diff-QoP) scheme where different levels of protection are provided. In this context, we investigate on two different power-reduction strategies to be used in protected WDM networks: (i) setting backup devices into low-power modes (sleep mode) and (ii) adapting the devices (i.e., transmitting/receiving equipment) usage to hourly traffic variations. We present exact modeling through Integer Linear Program (ILP) of the three scenarios and a provisioning algorithm to solve the problem of power minimized design of resilient optical core networks, under static and dynamic traffic conditions. We evaluate the performance of the proposed algorithm under static traffic conditions by comparing the obtained results with the optimal solution, in absence of traffic grooming. We show that the proposed heuristic reduces the computational time by three orders of magnitude with an optimality gap ranging from 8.88 up to 23.88%. Furthermore, we include traffic grooming and solve the problem under dynamic traffic conditions. Our findings show that enabling sleep mode (SM) for backup devices can help reduce total power consumption up to 20 and up to 38% when considering with Diff-QoP. Finally, adapting the number of transmitting/receiving devices to actual traffic needs guarantees power savings up to 80%, especially during off-peak hours.

A routing and wavelength assignment scheme considering full optical carrier replication in multi-carrier-distributed optical mesh networks with wavelength reuse

This paper proposes a routing and wavelength assignment (RWA) scheme that considers full optical carrier replication to minimize the number of required wavelengths for wavelength-reusable multi-carrier-distributed (WRMD) mesh networks. Unlike the conventional wavelength division multiplexing networks where each node contains multiple laser diodes, the WRMD networks use a light source, called the multi-carrier light source, to ease the difficulty of controlling many light source devices. The optical carrier replication at any node of optical carrier or any end node of lightpath, called full optical carrier replication, improves the performance of the conventional schemes, which do not consider full optical carrier replication. This paper first formulates the RWA problem considering full optical carrier replication as an integer linear programming problem that minimizes the number of required wavelengths to satisfy the given lightpath setup requests. A heuristic RWA scheme is then proposed to solve the RWA problem in practical times. Simulation results show that our proposed heuristic RWA scheme for the WRMD network achieves a near-optimum number of wavelengths. In addition, it is able to reduce the number of required wavelengths for lightpath establishment, compared to the conventional scheme.

Maximization Network Throughput Based on Improved Genetic Algorithm and Network Coding for Optical Multicast Networks

AbstractMaximal multicast stream algorithm based on network coding (NC) can improve the network’s throughput for wavelength-division multiplexing (WDM) networks, which however is far less than the network’s maximal throughput in terms of theory. And the existing multicast stream algorithms do not give the information distribution pattern and routing in the meantime. In the paper, an improved genetic algorithm is brought forward to maximize the optical multicast throughput by NC and to determine the multicast stream distribution by hybrid chromosomes construction for multicast with single source and multiple destinations. The proposed hybrid chromosomes are constructed by the binary chromosomes and integer chromosomes, while the binary chromosomes represent optical multicast routing and the integer chromosomes indicate the multicast stream distribution. A fitness function is designed to guarantee that each destination can receive the maximum number of decoding multicast streams. The simulation results showed that the proposed method is far superior over the typical maximal multicast stream algorithms based on NC in terms of network throughput in WDM networks.

Hardware-Efficient Adaptive Equalization and Carrier Phase Recovery for 100-Gb/s/λ-Based Coherent WDM-PON Systems

We propose a 100-Gb/s/λ-based coherent wavelength division multiplexing passive optical network system with a hardware-efficient digital signal processing (DSP), which features a new adaptive equalization (AEQ) and carrier phase recovery (CPR). While a conventional AEQ consists of four finite impulse response (FIR) filters in a butterfly configuration, we propose to split the conventional AEQ into a 1-tap butterfly FIR filter and two nonbutterfly FIR filters to halve the number of long FIR filters, sacrificing compensation of differential group delay (DGD). To reduce the complexity of the CPR, we propose to replace the phase estimation of one of the two polarizations by the less computation-intensive estimation of the phase offset between the two polarizations, since the phase noises of the two polarizations are almost identical. With the proposed AEQ and CPR, the number of multiplications is reduced by 41% compared with more conventional cases. An 80-km downstream transmission experiment with 32 Gbaud dual-polarization quadrature phase-shift keying (DP-QPSK) signals and offline DSP showed that our proposed system achieved a loss budget of 40.7 dB capable of supporting 8 ONU splits over an 80-km single-mode fiber span. The tolerance to DGD is evaluated by numerical simulation, and the results revealed that the penalty from DGD was less than the margin obtained in the transmission experiment.

Computing approximate blocking probabilities for transparent waveband switching based WDM networks using hierarchical cross-connects

An analytical model is presented to study the dynamics of wavelength division multiplexing (WDM) networks with waveband switching (WBS). The reduced load approximation method is considered to compute approximated network blocking probabilities in WBS-based WDM networks. The analytical model considers the link blocking probability due to insufficient link capacity and an impact of the waveband granularity (G). The analytical model also considers the node blocking probability due to unavailability of a switch port at the wavelength cross connect (WXC) layer of an Hierarchical cross connect (HXC) switch node. The set of nonlinear equations is obtained with the link independence assumption and solved using repeated substitutions. The accuracy of the analytical model is examined by comparing with simulation results considering the random-fit algorithm for waveband and wavelength assignments in different network scenarios. Lightpaths are routed between source and destination (s-d) HXC switch nodes using shortest path first (SPF) routing. An impact of the switch parameter to limit the input and the output WXC switch ports of an HXC switching node is also being investigated using the analytical model as well as through simulation results.

Radar signal transmission and switching over optical networks

In this paper, we experimentally demonstrate a radar signal distribution over optical networks. The use of fiber enables us to distribute radar signals to distant sites with a low power loss. Moreover, fiber networks can reduce the radar system cost, by sharing precise and expensive radar signal generation and processing equipment. In order to overcome the bandwidth challenges in electrical switches, a semiconductor optical amplifier (SOA) is used as an all-optical device for wavelength conversion to the desired port (or channel) of a wavelength division multiplexing (WDM) network. Moreover, the effect of chromatic dispersion in double sideband (DSB) signals is combated by generating optical single sideband (OSSB) signals. The optimal values of the SOA device parameters required to generate an OSSB with a high sideband suppression ratio (SSR) are determined. We considered various parameters such as injection current, pump power, and probe power. In addition, the effect of signal wavelength conversion and transmission over fiber are studied in terms of signal dynamic range.

Digital Linearization of Direct-Detection Transceivers for Spectrally Efficient 100 Gb/s/λ WDM Metro Networking

Single-polarization, single-photodiode-based direct-detection (DD) transceivers offer advantages for metro networks due to their simple and low-cost optical hardware structure. Single-sideband Nyquist-pulse-shaped subcarrier modulation (SSB Nyquist-SCM) is a promising signal format to achieve high information spectral density (ISD) in such DD systems. In this paper, we present theoretical and experimental evaluations of a variety of direct-detection SSB Nyquist-SCM system designs, operating at 100 Gb/s per wavelength in wavelength division multiplexing (WDM) metro network scenarios. Through simulations, several receiver-based digital linearization techniques to overcome the effect of signal-signal beat interference were investigated, and their performance compared with alternative approaches, including optical beat-interference cancellation receivers (BICRx) and coherent receivers (both heterodyne and homodyne). Subsequently, experimental assessments of the digitally-linearized DD receivers were carried out. Spectrally efficient (net ISD exceeding 3 b/s/Hz) 4 × 112 Gb/s WDM DD single-sideband 16-QAM Nyquist-SCM transmission over distances of up to 240 km (multi-span links) and 160 km (single-span links without mid-span amplification) were shown to be possible using uncompensated standard single-mode fiber.

Methods for Low Crosstalk and Wavelength Tunability in Arrayed-Waveguide Grating for On-Silicon Optical Network

Arrayed waveguide gratings (AWGs) are used to accomplish complex functionalities in dense wavelength division multiplexing networks, as well as in signal processing, measurement, characterization or sensing. In this work, we discuss the design and the experimental characterization of a 6 × 400 GHz channel-spaced AWG to be used as wavelength multiplexer/demultiplexer in a silicon-on-insulator based optical transport network. We adopted a whiskered-shaped star coupler design to investigate how the reduction in the reflectivity of the free propagation region boundaries affects the overall performances of the AWG. We demonstrated 2.9 dB insertion loss, which does not include fiber coupling loss, and ( $-24.4\,\pm \,0.1$ ) dB crosstalk for a design realized with a single etching technique. Moreover, we demonstrated an efficient fine-tuning (7.5 nm/W) of the spectral position of the AWG output channels.

Cross-phase modulation mediated pulse control with Airy pulses in optical fibers

We show that the velocity and thus the frequency of a signal pulse can be adjusted by the use of a control Airy pulse. In particular, we utilize a nonlinear Airy pulse which, via cross-phase modulation, creates an effective potential for the optical signal. Interestingly, during the interaction, the signal dispersion is suppressed. Importantly, the whole process is controllable and by using Airy pulses with different truncations leads to predetermined values of the frequency shifting. Such a functionality might be useful in wavelength division multiplexing networks.

Resource Assignment Strategy in Optical Networks Integrated With Quantum Key Distribution

Data transmission with optical fiber is vulnerable to eavesdropping. Moreover, conventional key distribution technology suffers from increasing computational power and upgraded attack algorithms. To address these issues, quantum key distribution (QKD), a quantum technology that secures secret information (such as a cryptographic key) exchange between two parties, can be used to guarantee secure data transmission. Integrating QKD into existing wavelength division multiplexing optical networks has been verified through a series of experiments, which contribute to ensuring network security and saving fiber resources. This paper addresses the resource assignment problem in QKD-enabled optical networks. First, a QKD-enabled optical network architecture is introduced. A small fraction of wavelength channels are segmented into multiple time slots with optical time division multiplexing technology to construct quantum key channels (QKChs) and measuring-basis channels, and then the remaining wavelengths can construct traditional data channels. Second, a static routing, wavelength, and time-slot assignment (RWTA) strategy is proposed and verified by the integer linear programming formulation and a heuristic algorithm. In the RWTA, QKChs are assigned for service requests according to the security levels specified by relevant key-updating periods. Thus, the secret keys for data encryption can update periodically to enhance security. Simulation results indicate that there is a trade-off between security (i.e., security levels and security-level types) and resource utilization.

Virtual Carrier-Assisted DD-MB-OFDM Schemes for UDWDM Metro-Access Networks With Improved Tolerance to Four-Wave Mixing

Virtual carrier (VC)-assisted multiband orthogonal frequency division multiplexing (MB-OFDM) schemes with improved tolerance to the four-wave mixing (FWM) effect in direct-direction ultradense wavelength division multiplexing metro-access networks are proposed and discussed. The best scheme is identified from a set of alternative schemes chosen with potential to increase the tolerance to the FWM effect in VC-assisted MB-OFDM systems. A data rate per band and per user of the metro-access network of 10 and 25 Gb/s is considered for band spacings of 3.125 and 6.25 GHz, respectively. With the proposed MB-OFDM schemes, increase of the maximum acceptable power launched into the fiber can be achieved. This increase translates into a similar power budget (PB) improvement. With band spacings of 3.125 GHz, a PB improvement of 3 dB is achieved, which enables to double the number of users served by the metro-access network or to extend the reach of the optical distribution network (ODN) by about 12 km. For a 6.25-GHz band spacing, a PB improvement exceeding 4 dB is achieved, enabling to double the number of users and simultaneously extend the ODN coverage by about 5 km.

Elastic Versus WDM Networks With Dedicated Multicast Protection

We consider the routing and spectrum allocation (RSA) problem of protecting all-optical multicast sessions against a single link failure in elastic optical networks (EONs). A tree is derived to support a multicast session and can be considered as a set of paths originating from a common source. We use a scheme to protect each of the paths by an arc-disjoint backup path in the case of any link failure. For this problem, we provide a node-arc integer linear programming (ILP) formulation and propose a heuristic algorithm for this protection scheme. We evaluate the improvement achieved by the flexible grids adopted in EONs over the fixed-grid wavelength-division multiplexing (WDM) networks. The evaluation is done by considering static modeling based on ILP and heuristics as well as dynamic simulations. We consider two approaches for heuristic algorithms: one is a two-step (TS) approach that computes the routing trees then allocates spectrum. The other uses the spectrum window plane (SWP) and constructs auxiliary graphs for the relevant range of spectrum to jointly solve the RSA problem. We evaluate the performances of the proposed algorithms under static and dynamic traffic models. Based on the studied scenarios, we observe consistent improvement in efficiency of flexible grid EONs over fixed-grid WDM networks. Moreover, we demonstrate that the network size (likely because of the availability of more alternative routes) can significantly affect the benefit in efficiency achieved by the SWP-based approaches over the TS approaches.

Leveraging the Survivable All-Optical WDM Network Design With Network Coding Assignment

This letter investigates a novel use of network coding (NC) in 1 + 1 protection for transparent wavelength-division multiplexing networks by utilizing a cost-effective all-optical XOR encoder/decoder. In applying this scheme, we introduce a new problem, called routing, wavelength, and NC assignment, and formulate it as the integer linear programming model, aiming at maximizing the network throughput under constrained bandwidth capacity. We evaluate our proposal on the realistic topology, COST239, with all-to-one traffic setting. The numerical results on studied case show that the our NC-based approach could support up to 30% traffic more than the conventional 1 + 1 protection.

Performance Analysis of Hybrid Fiber/FSO Backhaul Downlink over WDM-PON Impaired by Four-Wave Mixing

Abstract In this paper, we examine the hybrid optical fiber (OF)/free-space optics (FSO) architecture for a backhaul downlink over a wavelength-division multiplexing passive optical network (WDM-PON). The hybrid backhaul architecture is able to provide not only high-data-rate but also flexibility and quick deployment. The performance analysis is carried out for the hybrid OF/FSO backhaul downlink over a four-wavelength WDM-PON under the effect of four-wave mixing (FWM). The impact of atmospheric turbulence-induced fading and major noise components, including amplifier’s noise, shot noise, beat noise, background noise, and thermal noise, is also taken into account. The numerical results show that, although high transmitted power and amplifier’s gain at the transmitter side help to mitigate the impact of noise and fading, they should be limited to a specific value to avoid the influence of FWM. Therefore, the use of amplifier or avalanche photodiode at the receiver side would be a better solution to keep the bit-error rate (BER) at the low levels.

Wide-sense nonblocking multicast in optical WDM networks

Multicast communication is the concurrent transmission of data from one source node to many destination nodes. It is widely deployed in high performance computing and communication networks. In this article, wide-sense nonblocking multicast communication is studied in wavelength division multiplexing networks namely modified linear array, unidirectional and bidirectional modified ring networks. The sufficient and necessary condition on the minimum wavelength number required for the network to be wide-sense nonblocking is derived for each of the above network topologies under longest link first routing technique which employs approximately half the number of hops when compared with networks without modification. An explicit wavelength allotment technique for multicast assignment is also given for each of the above network topologies.