Wavelength Division Multiplexing Networks Research Articles

Physical topology optimization for highly reliable and efficient wavelength-assignable optical networks

Optical networks, such as wavelength-division multiplexing networks and elastic optical networks, require high reliability and efficient wavelength allocation. We propose a new physical topology optimization method that achieves both high reliability and efficient wavelength allocation. We compare the results of conventional algebraic connectivity optimization, which discusses physical topology optimization from the viewpoint of spectral graph theory, with those based on reliability optimization, which is important from the viewpoint of network operations. From the comparison analysis, it is shown that our proposed two-step degree bounded reliability-optimization model, which optimizes reliability with appropriate node degree constraints, leads to a physical topology that has high wavelength capacity without compromising reliability.

WDM-PON Management and Control by Auxiliary Management and Control Channel for 5G Mobile Fronthaul

The demand for fifth generation (5G) mobile systems has been exploding. There are strict latency and transmission capacity requirements, especially in the optical fiber section called the mobile fronthaul. A wavelength division multiplexing passive optical network (WDM-PON) system is an attractive solution to accommodate the high demand of traffic. However, wavelength management, which is important in a WDM-PON system, has not been sufficiently studied at the system level. In previous studies, control by a management control channel independent of the client signal, called the auxiliary management and control channel (AMCC), has been considered in many cases. In most of these studies, physical layer evaluation, such as the effect of superimposing the management control channel, was conducted for feasibility studies, and it was only confirmed that the effect was minor by measuring the bit error rate. In this paper, we review and compare the superimposition schemes of the AMCC to clarify operating conditions such as modulation format and modulation index of the AMCC signals. In addition, we propose a WDM-PON system managed using AMCC for ONU activation, wavelength adjustment and alive monitoring. We then discuss the connection of a WDM-PON prototype system we developed to a 5G mobile system to evaluate the effect of throughput on user equipment. The results indicate that the WDM-PON prototype system did not degrade (less than 2%) the downlink throughput even when the wavelength adjustment function was used against wavelength drift.

Joint Symbol Rate-Modulation Format Identification and OSNR Estimation Using Random Forest Based Ensemble Learning for Intermediate Nodes

In this paper, a novel joint symbol rate-modulation format identification (SR-MFI) and optical signal-to-noise ratio (OSNR) estimation scheme using the low-bandwidth coherent detecting and random forest (RF)-based ensemble learning is proposed for intermediate nodes in the flexible dense wavelength division multiplexing (F-DWDM) networks. By leveraging low-bandwidth coherent detecting with small bulk wavelength scanning, no chromatic dispersion compensation and low-complexity RF, the proposed scheme could serve as a reduced-complexity and cost-effective option to realize joint SR-MFI and OSNR estimation at intermediate nodes in F-DWDM networks. To verify the feasibility of the proposed scheme, the comprehensive simulations of 8/16 GBaud polarization division multiplexing (PDM)-4/16/32/64 quadrature amplitude modulation (QAM) systems are conducted. The simulation results show that the identification accuracy of SR-MFI reaches 100% and the mean absolute error of OSNR estimation is within 1 dB. Moreover, the proposed monitoring scheme is verified by 8/16 GBaud PDM-4/16/32QAM coherent transmission experiments.

Learning to Classify DWDM Optical Channels from Tiny and Imbalanced Data.

Applying machine learning algorithms for assessing the transmission quality in optical networks is associated with substantial challenges. Datasets that could provide training instances tend to be small and heavily imbalanced. This requires applying imbalanced compensation techniques when using binary classification algorithms, but it also makes one-class classification, learning only from instances of the majority class, a noteworthy alternative. This work examines the utility of both these approaches using a real dataset from a Dense Wavelength Division Multiplexing network operator, gathered through the network control plane. The dataset is indeed of a very small size and contains very few examples of “bad” paths that do not deliver the required level of transmission quality. Two binary classification algorithms, random forest and extreme gradient boosting, are used in combination with two imbalance handling methods, instance weighting and synthetic minority class instance generation. Their predictive performance is compared with that of four one-class classification algorithms: One-class SVM, one-class naive Bayes classifier, isolation forest, and maximum entropy modeling. The one-class approach turns out to be clearly superior, particularly with respect to the level of classification precision, making it possible to obtain more practically useful models.

10-Gb/s data transmission using optical physical layer encryption and quantum key distribution

A 10-Gb/s data transmission using the optical physical layer encryption and quantum key distribution (QKD) is developed. The physical layer encryption basing on the spectrum phase encoding technology, and the quantum key distribution relying on optical intensity modulation (IM) Y-00 cipher, are together performed to secure optical transmissions at 10 Gb/s. Especially, We propose a quantum key distribution method in which the encryption key generated at a update rate of up to 10 MHz is used for the parameters of the physical layer encryption with the spectral phase encoding. Compared with traditional quantum key distribution, our key rate is out of reach. A 10-Gb/s secure prototype is developed basing on this technique, which is experimentally applied in the 20-channel wavelength division multiplexing (WDM) network over 100 km fiber. The experimental results show that this method can ensure reliable transmission of cooperative users and prevent information from eavesdropping. The power penalty caused by data encryption is less than 3 dB for improving security of the data transmission. Furthermore, the bit error rate (BER) is analyzed, a BER above 0.48 for eavesdropper is verified.

Efficient solution for WDM-PON with low value of BER using NRZ modulation

Abstract This paper focused on the novel design of receiver side of wavelength division multiplexing passive optical network (WDM-PON). It serves the need for a dramatic change in demand for high data rate beyond 10 gigabits per second (Gbps) at the last mile for a larger coverage area or distance. This increase in demand for higher bandwidth is due to the emerging future technologies like Internet of things (IoT), silicon on chip (SoC), cloud computing, machine learning (ML), and artificial intelligence (AI). Simulation results demonstrated for the different coverage areas which compare the bit error rate (BER), quality (Q)-Factor, and eye height as per the guidelines of ITU-T. It has been predicted that the proposed WDM-PON design supports up to a distance of 60 km. Results have been verified for 40 km, 50 km, 60 km, and 70 km, respectively, at 100 GHz frequency spacing with acceptable BER and better quality (Q)-factor as defined by ITU.

Resource-aware provisioning strategies in translucent elastic optical networks

Elastic optical networks (EONs) enable a more efficient use of spectrum resources than traditional wavelength-division multiplexing (WDM) networks, mainly by means of a flexible frequency grid and the use of bandwidth variable transponders (BVTs). In WDM networks, regeneration is avoided because it always produces a cost increase and it is only recommended when the transmission length cannot be met. Instead, in EONs, a trade-off exists between regeneration and spectrum use. Indeed, blocking probability can be widely reduced by incorporating regeneration (BVTs in a back-to-back configuration) to shorten the transmission lengths, therefore increasing spectrum efficiency. Provisioning algorithms that take into account this trade-off consider regeneration either as a cost to be minimized (full regeneration capacity) or as a resource to be smartly used (bounded number of predeployed transponders).In recent years, algorithms that minimize the resource use of either spectrum or BVT have been proposed. These algorithms, however, penalize the overall network performance in terms of blocking probability and cost, since they do not take into account the available resources. In this work, we propose two novel resource-aware algorithms, that take into account all available resources in the provisioning process. We report simulation results showing that using these resource-aware algorithms: (i) when full regeneration capacity is assumed, the regeneration cost can be reduced by more than a 30% compared to the opaque solution and by a 10% compared to the best known algorithms; (ii) for the bounded case, resource-aware strategies can reduce blocking probability by thousands of times compared to the transparent solution and by hundreds of times compared to the best known algorithms. Our results show that resource awareness helps to decrease the blocking probability while increasing the actual network capacity, thanks to a more efficient assignment of both spectrum and BVT resources.

Novel analysis of blocking probability along with topologies of WDM Passive Optical Network

A novel analysis of blocking probability has been studied along with topologies. It has been shown that the algorithm proposed offers the minimum probability of blocking. The performance of wavelength division multiplexing passive optical network (WDM-PON) has been studied for different values of loads. To analyze the blocking probability, conventional algorithms have been used i.e. random and first-fit wavelength assignment using different number of wavelengths. It elaborates the proposed WDM-PON network in order to serve all ONUs providing the bandwidth as required by each ONU or end user. Performance of the system has been investigated using the quality parameters like signal-to-noise ratio (SNR), bit error rate (BER) and eye diagram. The result elaborates the performance of proposed algorithm which offers the least blocking probability. At last, study introduces different challenges and aspects of future needs in formulating an effective WDM PON system.

Flexible non-linear physical security coding scheme combined with chaotic neural network for OFDM-WDM-PON.

In this paper, a flexible physical security coding scheme integrating chaotic neural network (CNN) and non-linear encryption is proposed for orthogonal frequency division multiplexing wavelength division multiplexing passive optical network (OFDM-WDM-PON). The scheme improved the flexibility, adjustability and the key space of chaotic encryption system by introducing chaos into neural networks. The system will encrypt the bit series, probability shaping points, and subcarriers position of the OFDM signal through linear encryption and non-linear encryption concurrently. Results show that a key sensitivity of 10-15 and a key space of more than 10279 can be achieved. The encrypted system's Lyapunov is 5.2631, along with 12 parameters can be dynamically changed in the range of 0∼5. Furthermore, when the bit error rate (BER) is less than 3.8×10-3, probabilistic shaping (PS) technology decreases power loss by around 0.5 dB. A 20.454 Gb/s data transmission experiment was successfully verified for a span of 25 Km single-mode fiber. According to the experimental results, the proposed encryption scheme is likely to be used in future OFDM-WDM-PON transmission systems.

Design and control of highly spectrally efficient photonic networks enabled by fiber-granular routing on overlaid ring-shaped topologies

We propose an ultradense wavelength-division-multiplexing (WDM) network architecture that dramatically enhances channel accommodation density to achieve extremely high spectral efficiency. The trade-offs between high spectral efficiency and severe signal impairment due to optical filtering are resolved by network optimization of the overlaid subnetworks based on fiber-granular routing and wavelength-granular add/drop operations. The spectrum narrowing induced by node operations is well controlled by the impairment-suppressing routing and wavelength assignment (RWA) method. Numerical simulations on several metro-scale network topologies verify that the proposal enhances the spectral efficiency by up to 31.0% compared to comparable dense WDM networks.

A high-reliability optical network architecture based on wavelength division multiplexing passive optical network

A high-reliability optical network architecture based on wavelength division multiplexing passive optical network

Joint routing, link capacity dimensioning, and switch port optimization for dynamic traffic in optical networks

This paper considers a challenging problem: to simultaneously optimize the cost and the quality of service in opaque wavelength division multiplexing (WDM) networks. An optimization problem is proposed that takes the information including network topology, traffic between end nodes, and the target level of congestion at each link/node in WDM networks. The outputs of this problem include routing, link channel capacities, and the optimum number of switch ports locally added/dropped at all switch nodes. The total network cost is reduced to maintain a minimum congestion level on all links, which provides an efficient trade-off solution for the network design problem. The optimal information is utilized for dynamic traffic in WDM networks, which is shown to achieve the desired performance with the guaranteed quality of service in different networks. It was found that for an average link blocking probability equal to 0.015, the proposed model achieves a net channel gain in terms of wavelength channels ( ) equal to 35.72 , 39.09 , and 36.93 compared to shortest path first routing and equal to 29.41 , 37.35 , and 27.47 compared to alternate routing in three different networks.

Cost-efficient routing, modulation, wavelength and port assignment using reinforcement learning in optical transport networks

With the rapid growth of global network traffic, more and more high-capacity network services are required. Traditional wavelength division multiplexing (WDM) networks are inadequate in terms of service scheduling and network management, so optical transport networks (OTN) have been proposed. OTN offers electric-layer switching ability to support finer granularity and higher spectrum efficiency. In OTN, we need to realize routing, modulation, wavelength, and port assignment (RMWPA) for supporting optical-electric (O/E) conversion (i.e., O/E port). Efficient RMWPA will significantly reduce the cost of operators. In this paper, we explore multi-modal information from OTN, and image the topology and routes to capture the information of the OTN and services. We design a cost-efficient RMWPA (CE-RMWPA) algorithm based on reinforcement learning to realize RMWPA for reducing cost in OTN. The proposed algorithm can interact with the OTN environment and learn how to make improved decisions based on the environment’s feedback. Simulative results demonstratethat the CE-RMWPA algorithm can achieve the optimization of RMWPA for reducing cost.

Performance of Injection-Locked Quantum-Dash MMW Source Under Clear and Dusty Weather Conditions

We report on the generation and transmission of 30 GHz millimeter-wave (MMW) beat-tone signals employing external- (EIL) and self-injection-locked (SIL) InAs/InP quantum-dash based dual-wavelength laser (QD-DWL) sources emitting in mid L-band. Later, successful transmission of 2 Gbps quadrature phase-shift-keying (QPSK) signal over clear weather conditions on 2 m wireless (WL), and hybrid channels consisting of 20 km single-mode fiber (SMF) and 2 m WL, and 20 km single-mode fiber (SMF), 5 m free-space-optics (FSO) and 2 m WL, are demonstrated employing both MMW sources, with a slight ∼1.4 dBm extra received optical power requirement from SIL QD-DWL. Lastly, examining the effect of dusty weather conditions on the MMW transmission over 20 km SMF, 0.9 m FSO and 1 m WL hybrid channel, considering both EIL and SIL sources, showed maximum visibility range (V) of 12 ± 2 m and 16 ± 2 m for successful transmission, respectively. These investigations reinforce the simple, cost-effective, and energy-efficient SIL QD-DWL as a candidate L-band millimeter-wave (MMW) source compared to the EIL counterpart in 5G and next-generation radio-over-fiber wavelength-division multiplexing networks.

2 Tbit/s based coherent wavelength division multiplexing passive optical network for 5G transport

2 Tbit/s based coherent wavelength division multiplexing passive optical network for 5G transport

Spectral processing techniques for efficient monitoring in optical networks

Having ubiquitous optical monitors in dense wavelength-division multiplexing (DWDM) or flex-grid networks allows the estimation in real time of crucial parameters. Such monitoring would be even more important in disaggregated optical networks, to inspect performance issues related to inter-vendor interoperability. Several important parameters can be retrieved using optical spectrum analyzers (OSAs). However, omnipresent OSAs represent an infeasible solution. Nevertheless, the advent of new, relatively cheap, compact and medium-resolution optical channel monitors (OCMs) enable a more intensive deployment of these devices. In this paper, we identify two main scenarios for the placement of such monitors: at the ingress and at the egress of the optical nodes. In the ingress scenario, we can directly estimate the parameters related to the signals, but not those related to the filters. On the contrary, in the egress scenario, the filter-related parameters can be easily detected, but not those related to amplified spontaneous emission. Therefore, we present two methods that, leveraging a curve fitting and a machine learning regression algorithm, allow detection of the missing parameters. We verify the proposed solutions with spectral data acquired in simulation and experimental setups. We obtained good estimation accuracy for both setups and for both studied placement scenarios. It is noteworthy that in the experimental assessment of the ingress scenario, we achieved a maximum absolute error (MAE) lower than 1 GHz in filter bandwidth estimation and a MAE lower than 0.5 GHz in filter frequency shift estimation. In addition, by comparing the relative errors of the considered parameters, we identified the ingress scenario as the more beneficial. In particular, we estimated the filter central frequency shift with 84% and the filter 6 dB bandwidth with 75% higher accuracy, with respect to datasheet/reference values. This translates into a total reduction of the estimated signal-to-noise ratio (SNR) penalty, introduced by a single optical filter, of 0.24 dB.

Pre-Filtering Techniques for Spectrum Narrowing Caused by Optical Node Traversal in Ultra-Dense WDM Networks

To improve the spectral efficiency and increase network capacity, wavelength signals must be multiplexed densely, i.e., ultra-dense wavelength-division-multiplexing (WDM) networks. However, the spectrum of each WDM signal is narrowed by the wavelength-selective switches placed in optical nodes, so the transmissible distance and node hop count of the signal are strictly limited. To counter this spectrum narrowing problem caused by optical node traversal in ultra-dense WDM networks, pre-filtering techniques have been proposed. This paper comprehensively investigates the performance of four pre-filtering techniques: conventional Nyquist filtering, pre-emphasis filtering, partial-response filtering, and the combination of pre-emphasis and partial-response filtering. We conduct extensive computer simulations and discuss the optimality of pre-filtering techniques. The simulation results show that the adaptive use of pre-filtering can substantially extend the maximum attainable transmission distance and hop counts of 4/16/64-QAM signals.

8 × 10 Gb/s Downstream PAM-4 Transmission for Cost-Effective Coherent WDM-PON Application

We experimentally demonstrate digital signal processing (DSP)-free 8 × 10 Gb/s 4-level pulse-amplitude modulation (PAM-4) transmission for cost-effective coherent wavelength division multiplexing passive optical network (WDM-PON) with 20 GHz channel spacing over the C-band. The polarization-independent coherent receiver at optical network unit (ONU) including a 3 × 3 fiber coupler and a polarization beam splitter (PBS) followed by three single-ended photodiodes (PDs), is simple and cost-effective, because neither DSP nor phase/frequency locking is necessary for the coherent detection of PAM-4 signal. We numerically compare the performance between the transmitted signal diversity and the local oscillator (LO) signal diversity schemes, and optimize the parameters of heterodyne detection, in order to enhance the power budget. Based on the LO signal diversity scheme, we can achieve an average receiver sensitivity of -26 dBm for eight wavelength channels at a bit error ratio (BER) below the hard-decision forward error correction (HD-FEC) threshold (i.e., 3.8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> ), leading to a power budget of 29 dB after 25 km standard single-mode fiber (SSMF) transmission. Moreover, we verify an unequally spaced PAM-4 signaling, leading to contribution of 1 dB receiver sensitivity improvement for 10 Gb/s/λ PON.

Auxiliary-Graph-Based Energy-Efficient Traffic Grooming in IP-Over-Fixed/Flex-Grid Optical Networks

Due to the development of broadband access technologies including FTTx and 5G, the traffic in metro and core networks is forecasted to be more dynamic. To support this dynamicity, flex-grid elastic optical networks (EONs) have started to become prolific over the past few years. During the migration from the legacy fixed-grid wavelength division multiplexing optical networks to flex-grid EONs, a transition technology called the fixed/flex-grid optical network has become popular. In such fixed/flex-grid networks, the energy consumption caused by serious capacity mismatch between variable IP traffic and the different optical channel capacities is significantly high to be ignored. In fact, energy-efficient traffic grooming (i.e., to aggregate multiple fine-grained IP flows and map them onto a lightpath) is a challenge in IP-over-fixed/flex-grid optical networks because co-existing fixed-grid and flex-grid nodes have different traffic grooming ability and energy consumption models. To overcome the challenge, we propose an auxiliary-graph-based energy-efficient traffic-grooming (EETG) algorithm in IP-over-fixed/flex-grid optical networks for the first time. The construction of an auxiliary graph (AG) model for each connection request is one of the core steps. The well-designed weight-assignment scheme of the AG establishes the relationships between traffic grooming operations and specific energy consumption models. The final traffic grooming operations are undertaken based on the calculated weight-minimized path. The simulation results show that the EETG algorithm achieves 1) the least energy consumption compared with the state-of-the-art traffic grooming algorithms under the non-blocking scenario; and 2) achieves the tradeoff between energy consumption and blocking probability under the blocking scenario.

Performance of subcarrier-wave quantum key distribution in the presence of spontaneous Raman scattering noise generated by classical DWDM channels

In this paper, we study the performance of the subcarrier-wave quantum key distribution system (SCW QKD) in the presence of spontaneous Raman scattering (SpRS) noise generated by classical channels of the dense wavelength division multiplexing (DWDM) network within a single-mode optical fiber. We present the mathematical model for evaluation of the quantum bit error rate and secure key generation rate with the SpRS noise taken into account. We consider two regimes of the SCW QKD system: the continuous wave regime, which uses a continuous wave laser, and the pulsed regime. For these regimes, performance of the system is analyzed depending on receiver sensitivity of classical DWDM. It is found that the pulsed regime outperforms the continuous wave regime in both the secure key generation rate and maximum achievable distance.