Wavelength Conversion Capability Research Articles

Multi-fidelity machine learning for predicting bandgaps of nonlinear optical crystals.

Nonlinear optical (NLO) materials are of great importance in modern optics and industry because of their intrinsic capability of wavelength conversion. Bandgap is a key property of NLO crystals. In recent years, machine learning (ML) has become a powerful tool to predict the bandgaps of compounds before synthesis. However, the shortage of available experimental data of NLO crystals poses a significant challenge for the exploration of new NLO materials using ML. In this work, we proposed a new multi-fidelity ML approach based on the multilevel descriptors developed by us (Z.-Y. Zhang, X. Liu, L. Shen, L. Chen and W.-H. Fang, J. Phys. Chem. C, 2021, 125, 25175-25188) and the gradient boosting regression tree algorithm. The calculated and experimental bandgaps of NLO crystals were collected as the low- and high-fidelity labels, respectively. The experimental values were predicted based on chemical compositions of crystals without prior knowledge about crystal structures. The multi-fidelity ML model overcame the performance of single-fidelity predictor. Furthermore, it was observed that less accurate predictions on the low-fidelity label may result in more accurate prediction on the high-fidelity label, at least in the present case. Using the multi-fidelity ML model with the best performance in this work, the mean absolute error on the test set of experimental bandgaps was 0.293 eV, which is smaller than that using the single-fidelity model (0.355 eV). It is far from perfect but accurate enough as an effective computational tool in the first step to discover novel NLO materials.

Simulation of Coherent Electromagnetic Waves in Wavelength Division Multiplexing (WDM) Transmission

This study analyzes the application of Wavelength Division Multiplexing (WDM) in fiber optic networks which aims to find the wavelength, WDM optical spectrum and modes, as well as the CPR estimated phase and modes. In this study WDM allows the simultaneous transmission of different data streams through a single optical fiber, using different wavelengths. This research was conducted using the python OptiCommPy module. This module is used to perform modeling of complex optical fiber transmission systems by considering the various parameters and disturbances involved in optical transmission. The results obtained from this study are that WDM networks can use full or limited wavelength conversion, depending on the wavelength conversion capability of each network node. Whereas multifiber networks use fiber pools between network nodes, and multifiber WDM networks can be implemented without or with full wavelength conversion. This research can be a guide for designing coherent electromagnetic waves in WDM transmissions using the OptiCommPy python module.

Wavelength Selective Switch-Based Clos Network: Blocking Theory and Performance Analyses

A Clos network is a classical switching network often used in conventional electrical switches. In a Wavelength Selective Switch (WSS) based Clos all-optical switching network, the wavelength dimension needs to be additionally considered. However, the conventional blocking theory of the Clos network may not be valid in this scenario and it may be necessary to conduct a theoretical study specifically for the WSS-based Clos all-optical switching network. In this paper, we derive the strictly non-blocking conditions for the WSS-based Clos network for the cases where there is no wavelength conversion, partial wavelength conversion, and full wavelength conversion. For the situation where there is service blocking, we also formulate probabilistic analytical models to estimate the blocking performance for the three types of WSS-based Clos networks. The gain of transceiver utilization achieved by the WSS-based Clos network with wavelength conversion is evaluated and compared with that of one without wavelength conversion. We also evaluate the impact of partial wavelength conversion capability on the blocking performance of a WSS-based Clos network.

Sub-Tree-Based Approach for Reconfiguration of Light-Tree Pair without Flow Interruption in Sparse Wavelength Converter Network

Network reconfiguration is an important mechanism for network operators to optimize network performance and optical flow transfer. It concerns unicast and multicast connections. Multicast connections are required to meet the bandwidth requirements of multicast applications, such as Internet Protocol-based TeleVision (IPTV), distance learning, and telemedicine. In optical networks, a multicast connection is made possible by the creation of an optical tree-shaped path called a light-tree. The problem of light-tree pair reconfiguration is addressed in this study. Given an initial light-tree used to transfer an optical flow and a final light-tree that is computed by the network operator to optimize network performance, the goal is to migrate the optical flow from the initial light-tree to the final light-tree without flow interruption. Flow interruption is not desirable for network operators because it forces them to pay financial penalties to their customers. To solve this problem, existing methods use a branch approach that is inefficient if some network nodes do not have wavelength conversion capability. Therefore, we proposed in this study a sub-tree-based method. This approach selects and configures sub-tree pairs from the light-tree pair (initial light-tree, final light-tree) to be reconfigured. Then, we produce a sequence of configurations. The performance study confirms that our method is efficient in solving the problem of light-tree pair reconfiguration because our method does not cause flow interruption.

Hybrid Algorithm Based Effective Light Trail Creation in an Optical Networks

Abstract With the overwhelming use of the Internet, the wavelength division multiplexing (WDM) optical networks have become the major mode of communication for wide applications. Hence, the routing and wavelength assignment (RWA) for a given traffic in WDM networks is the chief challenge in optical networks. This paper presents the RWA problem in WDM networks using the hybrid algorithm of flower pollination (FP) and simulated annealing (SA) algorithm (FA+SA) with and without wavelength conversion capability at the nodes of the network. Comparative analysis with techniques presented in literature is also carried out, i. e. differential evolution algorithm (DEA), firefly algorithm (FA), particle swarm optimization with less number of informers (Psolbest), SA and genetic algorithm (GA). The results prove that hybrid algorithm of FP and SA is potentially more efficient than algorithms present in literature for the light path establishment in an optical network.

Wide-sense nonblocking elastic optical switch

In this paper, we address the problem of wide-sense nonblocking operation of the elastic optical switch. The switch consists of waveband-converting switches in input and output stages, while in the center stage there is only one wavelength-selective space switch without wavelength-conversion capabilities. Two control algorithms are proposed, namely, 2-split and 3-split. For these algorithms we derived wide-sense nonblocking conditions and compared them with strict-sense nonblocking ones. The results show that the 3-split algorithm reduces the required number of FSUs to up to almost 70% of the FSUs required in the strict-sense nonblocking switching fabrics. Application of the proposed elastic optical switch in optical datacenter networks is also proposed.

Optical Packet Switching Architecture Using Wavelength Optical Crossbars

All-optical packet switching (OPS) is one of the promising technologies for the next generation of optical networks. It realizes the packet switching in optical domain that eliminates optical–electrical and electrical–optical conversions. One of the main components in an OPS network is the optical interconnect that provides the basic functionality of directing packets from input ports to the desired output ports, while maintaining data in the optical domain. Advances in all-optical technologies enable the wavelength exchanging phenomenon that can be used to develop new optical interconnect architectures. These architectures simultaneously combine the switching and the conversion domains. Thus, the use of the exchanging technology reduces the complexity without impacting the overall switching performance. In this paper, a new bufferless OPS interconnect by adopting wavelength optical crossbars that can combine both switching and wavelength conversion capabilities is proposed. The proposed architecture can operate in either of two modes: blocking or nonblocking. Our analysis to the proposed architecture confirms that, for the same number of input and output ports, a reduction in conversion and switching complexity can reached up to 50% and 99%, respectively, compared to traditional architectures.

PERFORMANCE ANALYSIS OF WSXC AND WIXC SSM OXC IN WDM OPTICAL NETWORKS

The impact of inband crosstalk on an optical signal passing through optical cross-connect nodes (OXC’s) in wavelength division multiplexing (WDM) optical network, is studied from the equation of electric field with crosstalk and the corresponding current. The analysis has been done for two SSM (space switching matrix) OXC architecture namely WSXC & WIXC where later one has full wavelength conversion capability. Although WIXC attenuates more crosstalk though it is found that depending on the values of optical propagation delay differences, coherent time of lasers and time duration of one bit of the signal, the required power penalty in WIXC may be greater than that of WSXC in some cases. The analysis has been performed on the measures of Bit Error Rate (BER) and Power Penalty.

A novel routing scheme in OBS network with sparse wavelength conversion capabilities

The overall burst loss probability is the primary metric of interest in an optical burst switching network with sparse wavelength conversion capabilities (SWCC-OBS). With the overall burst loss probability as the optimization objective, one has to solve an integer nonlinear programming (INLP) problem. In order to overcome the computational difficulties we propose a fictitious play method to approximately solve the INLP. Consequently, a randomized routing strategy can be achieved. The simulation results show that the proposed strategy can give a near-optimal route that avoids the conflict of burst data effectively and decreases the overall burst loss probability. At the same time it also performs well in balancing loads throughout the whole network under different kinds of burst traffic pattern.

Routing and wavelength assignment in all optical networks using differential evolution optimization

The routing and wavelength assignment (RWA) problem, known to be an NP-complete problem, seeks to optimally establish routes and adequate wavelengths for the requested connections according to an objective function. This paper presents the use of a novel approach based on a differential evolution (DE) algorithm to the RWA problem in wavelength-routed dense division multiplexing (DWDM) optical networks. The proposed DE-RWA algorithm is modeled to optimize not only the network wavelength requirement ( $$ NWR $$ N W R , which is the minimum number of wavelengths needed to fulfill traffic demand) but also the average path length ( $$ APL $$ A P L ). We present the impact of the control parameters of the DE algorithm on the improvement of system's performance. Additionally, we present two strategies to improve the efficiency of the algorithm, knowing as the disjoint cut-set paths (DCS-P) algorithm and the use of a random mutation ( $$ random -M$$ r a n d o m - M ) parameter for DE. The proposed approach is evaluated for test bench optical networks with up to 40 nodes. Experiments show that the DE-RWA algorithm obtains results that equal the $$ NWR $$ N W R lower bound for networks with and without wavelength conversion capability, whereas reduce the $$ APL $$ A P L . The performance of the DE-based approach is compared against results obtained with the particle swarm optimization (PSO) and genetic algorithm (GA) models, showing that the DE-RWA outperform those algorithms. The presented DE-RWA model is simple to implement and could also be extended by adding other features such as impairment-aware, energy efficient, survivability among others in optical networks.

Field Trial Demonstration of Spectrum Defragmentation and Grooming in Elastic Optical Node

A novel optical node architecture based on all-optical traffic grooming for flexible optical networks is proposed as a mean to utilize the optical spectrum flexibly. In this work, we have overcome the key technical challenge towards implementation of the node architecture by designing and experimentally evaluating a fully flexible intelligent optical node. The proposed solution has the potential to deal with simultaneous multi-functional degree of switching such as format conversion, wavelength conversion, multicasting, spectrum defragmentation and time-domain grooming capability in order to maintain efficient resource utilization. The field experiment was also performed on original and converted channels over a 110-km dark fiber link with the aim of proving the signal robustness in a real network scenario. Finally, BER measurements experimentally demonstrate efficient adaptive switching and processing of variable fragmented traffic, leading to improved network scalability and efficiency.

Performance Evaluation of an Optical Burst Switched Core Node With Generalized Arrivals and Partial Wavelength Conversion Capability

Many of the burst assembly algorithms employed in optical burst switching (OBS) networks preserve the IP traffic self-similarity property in the burst traffic. We introduce a mathematical model for performance evaluation of an OBS core node employing either no, a partial or a full wavelength conversion strategy. The model assumes long-range dependent (LRD) traffic arrivals to the OBS intermediate node whose inter-arrival times are accurately modeled by a Pareto distribution, whereas exponential holding times are assumed. In our proposed model, each output port in the node is modeled as a GI/M/w/w queue with partial server accessibility. An imbedded Markov chain approach is used to derive the limiting state probability distribution for the number of bursts currently served by an output port as seen by arriving bursts. Next, the average burst loss probability is evaluated from steady-state occupancy probabilities. In addition, the results of our mathematical model are validated via simulation. Furthermore, the results of the model are compared with those when assuming short-range dependent Poisson arrivals. Comparison shows that traditional Poisson traffic models yield over-optimistic performance measures compared to the LRD Pareto traffic models, especially for light traffic scenarios. Furthermore, we study the impact of varying different traffic parameters, such as the average arrival rate and the Hurst parameter, on the burst loss probability. Finally, the impact of varying the wavelength conversion capability on the burst loss probability is studied, where we compare two strategies for contention resolution: adding new channels (wavelengths) or adding wavelength converters, while taking the cost into consideration.

Dynamic Routing and Wavelength Assignment in Multifiber WDM Networks with Wavelength Conversion Capability

This paper proposes a dynamic routing and wavelength assignment (RWA) scheme in multifiber WDM networks with wavelength conversion capability. In multifiber WDM networks, each link consists of multiple fibers. Thus, multiple lightpaths with the same wavelength can be established in the same link as long as they use different fibers. In WDM networks with wavelength conversion, the network nodes have wavelength conversion capability which can convert one wavelength to another. In order to efficiently utilize multifiber and wavelength conversion capability, an appropriate RWA scheme is necessary. The proposed scheme provides RWA for multifiber WDM networks with sparse and full wavelength conversion capability. In the proposed scheme, a route and wavelengths are selected for each lightpath based on wavelength availability and location of nodes with wavelength conversion capability. Through simulation experiments, we show that the proposed scheme reduces the blocking probability of lightpath establishment efficiently.

부분적 광파장 변환 노드를 이용한 광인터넷 복구

This paper studies the effects of wavelength conversion on self-healing optical networks. We examined the effects of wavelength conversion capability on the backup routing and the spare wavelength utilization. The efficiency of spare wavelength utilization is proportionally increased as the wavelength conversion capability increases, different from the call blocking probability for which about 30% of wavelength conversion capability shows nearly the same performance as full wavelength conversion capability. The spare resource utilization efficiency can be improved by using alternate routing and wavelength assignment algorithms.

Fast Service Recovery Under Shared Protection in WDM Networks

In this paper, we investigate the problem of survivable routing of static demands in connection-oriented WDM networks with shared protection. We first discuss conditions and characteristics of a typical backup path sharing approach with respect to the average length of backup paths, and the values of connection restoration time. Next we propose a new method of sharing the backup paths, called SPGC, which is the first one that does not increase the length of backup paths (thus providing fast restoration of broken connections). The respective ILP model has been introduced. Owing to the complexity of the SPGC problem, an efficient heuristic algorithm designed for the general case of limited wavelength conversion capability has been also proposed. Extensive numerical experiments have shown that the proposed backup path sharing approach provides values of service recovery time which are up to 50% shorter on average, compared to the typical sharing technique. These results were achieved together with a significant reduction of the total link capacity utilization ratio of up to 40%.

A heuristic algorithm for lightpath scheduling in next-generation WDM optical networks

We study the routing and wavelength assignment (RWA) problem of scheduled lightpath demands (SLDs) in all-optical wavelength division multiplexing networks with no wavelength conversion capability. We consider the deterministic lightpath scheduling problem in which the whole set of lightpath demands is completely known in advance. The objective is to maximize the number of established lightpaths for a given number of wavelengths. Since this problem has been shown to be NP complete, various heuristic algorithms have been developed to solve it suboptimally. In this paper, we propose a novel heuristic RWA algorithm for SLDs based on the bee colony optimization (BCO) metaheuristic. BCO is a newborn swarm intelligence metaheuristic approach recently proposed to solve complex combinatorial optimization problems. We compare the efficiency of the proposed algorithm with three simple greedy algorithms for the same problem. Numerical results obtained by numerous simulations performed on the widely used realistic European Optical Network topology indicate that the proposed algorithm produces better-quality solutions compared to those obtained by greedy algorithms. In addition, we compare the results of the BCO---RWA---SLD algorithm with four other heuristic/metaheuristic algorithms proposed in literature to solve the RWA problem in the case of permanent (static) traffic demands.

A wavelength assignment algorithm for de Bruijn WDM networks

This paper proposes an offline wavelength assignment technique for de Bruijn (d, k) optical wavelength division multiplexing (WDM) networks having nodal degree d and diameter k that can support lightpaths between pair of nodes. Each lightpath uses a channel (wavelength) along each link in its route. An efficient algorithm is proposed that can be used to assign wavelengths to lightpath requests in O(k|V|) time, where |V| represents the number of nodes of the de Bruijn network and V represents the set of nodes. The proposed algorithm can be efficiently used for wavelength assignment in de Bruijn WDM networks having limited wavelength conversion capabilities. This work shows that de Bruijn graph can be expressed as union of edge-disjoint rings. Wavelengths are assigned for the individual rings in the graph thus resulting in the assignment for the graph itself. Results are shown for a given de Bruijn graph and for an arbitrary request. The proposed algorithm is compared with two other algorithms, which use two other known works of wavelength assignment on ring topology. Comparisons of the time complexity and the type of wavelength conversion required for these algorithms clearly show that the proposed algorithm is a faster and more efficient way of assigning wavelengths.

Performance analysis of topologies for optical wavelength convertible networks

An architecture of wavelength converters shared per-node wavelength cross-connects is proposed to function the optical node in simulation. And first-fit wavelength allocation algorithm and Dijkstra shortest path routing algorithm are used. It is shown that star topology performs the best on blocking probability, average hop count and average packet delay, but it is unfavorable on link utilization. Furthermore, wavelength conversion is not ideal for the star topology. However, the ring topology network is the cost-optimal one if the appropriate wavelength conversion capability in network is to be considered.

Performance analysis of multicast routing and wavelength assignment protocol with dynamic traffic grooming in WDM networks

The need for on-demand provisioning of wavelength-routed channels with service-differentiated offerings within the transport layer has become more essential because of the recent emergence of high bit rate Internet protocol IP network applications. Diverse optical transport network architectures have been proposed to achieve the above requirements. This approach is determined by fundamental advances in wavelength division multiplexing WDM technologies. Because of the availability of ultra long-reach transport and all-optical switching, the deployment of all-optical networks has been made possible. The concurrent transmission of multiple streams of data with the assistance of special properties of fiber optics is called WDM. The WDM network provides the capability of transferring huge amounts of data at high speeds by the users over large distances. There are several network applications that require the support of QoS multicast, such as multimedia conferencing systems, video-on-demand systems, real-time control systems, etc. In a WDM network, the route decision and wavelength assignment of lightpath connections are based mainly on the routing and wavelength assignment RWA. The multicast RWA's task is to maximize the number of multicast groups admitted or minimize the call-blocking probability. The dynamic traffic-grooming problem in wavelength-routed networks is generally a two-layered routing problem in which traffic connections are routed over lightpaths in the virtual topology layer and lightpaths are routed over physical links in the physical topology layer. In this paper, a multicast RWA protocol for capacity improvement in WDM networks is designed. In the wavelength assignment technique, paths from the source node to each of the destination nodes and the potential paths are divided into fragments by the junction nodes and these junction nodes have the wavelength conversion capability. By using the concept of fragmentation and grouping, the proposed scheme can be generally applied for the wavelength assignment of multicast in WDM networks. An optimized dynamic traffic grooming algorithm is also developed to address the traffic grooming problem in mesh networks in the multicast scenario for maximizing the resource utilization and minimizing the blocking probability. Copyright © 2011 John Wiley & Sons, Ltd.

Achieving 100% Throughput in Input-Buffered WDM Optical Packet Interconnects

Packet scheduling algorithms that deliver 100% throughput under various types of traffic enable an interconnect to achieve its full capacity. Although such algorithms have been proposed for electronic interconnects, they cannot be directly applied to WDM optical interconnects due to the following reasons. First, the optical counterpart of electronic random access memory (RAM) is absent; second, the wavelength conversion capability of WDM interconnects changes the conditions for admissible traffic. To address these issues, in this paper, we first introduce a new fiber-delay-line (FDL)-based input buffering fabric that is able to provide flexible buffering delay, followed by a discussion on the conditions that admissible traffic must satisfy in a WDM interconnect. We then propose a weight-based scheduling algorithm, named Most-Packet Wavelength-Fiber Pair First (MPWFPF), and theoretically prove that given a buffering fabric with flexible delay, MPWFPF delivers 100% throughput for input-buffered WDM interconnects with no speedup required. Finally, we further propose the WDM-i SLIP algorithm, a generalized version of the i SLIP algorithm for WDM interconnects, which efficiently finds an approximate optimal schedule with low time complexity. Extensive simulations have been conducted to verify the theoretical results, and test the performance of the proposed scheduling algorithms in input-buffered WDM interconnects.