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In software defined optical networks (SDON), a single controller can hardly manage all the optical devices especially in the large-scale networks, while multiple controllers deployed in the network can solve it. Recently, more and more attention has been paid to the multi-controller architecture, and the deployment of controllers is an important issue in large software defined optical networks. However, the existing architectures focus on static mapping of controllers and switches and do not consider load balance among different controllers. It is worth further studying the cooperation of multiple controllers. This paper presents a multi-controller coordinated deployment strategy (Switch Migration Based Controller Placement, SMBCP) based on load balancing. Simulation results show that SMBCP can significantly reduce the load difference among different controllers in SDON and reduce the migration cost of switches, thus improving the load balance of the controller.

Security threat is a challenging issue for data transmission in optical networks. Quantum key distribution (QKD) is a promising security solution to optical networks to provide secure keys. Meanwhile, key update is of importance to enhance the security of key in the networks. The previous update method is to provide a fixed key-updating period which has a strong regularity to be easily found. To enhance the security of data services, we proposed a quantum key-updating process by introducing the architecture of SDON secured by QKD. Then, a flexible quantum key-updating method (Flex-KUM) and a quantum key-updating algorithm based on Flex-KUM are designed in the comparison with the fixed method with different update periods. The results show that a higher level of security requires more updating keys, which leads to an increase in the blocking probability. Therefore, there is a trade-off between the enhanced security and resources.

As the significant infrastructure of the communication network, the security of the optical fiber is critical. Optical fiber eavesdropping is a common attack in optical communications, which can easily lead to leakage of information. To deal with this problem, this paper proposes a Machine Learning (ML)-based scheme to detect and locate physical-layer eavesdropping. To improve the efficiency and accuracy of eavesdropping detection, both Optical Performance Monitoring (OPM) data and eye-diagrams are adopted as input data. Three different ML classifiers are designed and tested to realize eavesdropping detection, location and split ratio recognition, respectively. To demonstrate the feasibility of the proposed scheme, an experiment is conducted in end-to-end fiber transmission system with Coherent Optical Orthogonal Frequency Division Multiplexing (CO-OFDM). The eavesdropping is simulated and performed by placing optical coupler in different positions. In addition, different splitting ratios are considered, including 95/5, 90/10. Results indicate that the ML scheme achieves 100% and 92.76% accuracy in eavesdropping detection and location, respectively.

In software defined optical networks (SDON), the centralized control plane may encounter numerous intrusion threatens which compromise the security level of provisioned services. In this paper, the issue of control plane security is studied and two machine-learning-based control plane intrusion detection techniques are proposed for SDON with properly selected features such as bandwidth, route length, etc. We validate the feasibility and efficiency of the proposed techniques by simulations. Results show an accuracy of 83% for intrusion detection can be achieved with the proposed machine-learning-based control plane intrusion detection techniques.

The spectrum fragmentation problem remains to be an open issue in elastic optical networks. In addition, the quality of service cannot be ignored during the transmission process. In this paper, we propose a novel spectrum defragmentation strategy considering the service differentiation, named SDSD, to improve the network performance in terms of the spectrum resources utilization, blocking probability (BP), and the set-up time for the serving connections. The presented results show that the proposed scheme can allocate the spectrum resources efficiently while decreasing the BP and connection set-up time. Moreover, the low grade services will be migrated preferentially during the phase of spectrum defragmentation, decreasing the number of migration.

With the capacity increasing in optical networks enabled by spatial division multiplexing (SDM) technology, spatial division multiplexing elastic optical networks (SDM-EONs) attract much attention from both academic and industry. Super-channel is an important type of service provisioning in SDM-EONs. This paper focuses on the issue of super-channel construction in SDM-EONs. Mixed super-channel oriented routing, spectrum and core assignment (MS-RSCA) algorithm is proposed in SDM-EONs considering inter-core crosstalk. Simulation results show that MS-RSCA can improve spectrum resource utilization and reduce blocking probability significantly compared with the baseline RSCA algorithms.

A proper traffic grooming strategy in dynamic optical networks can improve the utilization of bandwidth resources. An auxiliary graph (AG) is designed to solve the traffic grooming problem under a dynamic traffic scenario in spatial division multiplexing enabled elastic optical networks (SDM-EON) with multi-core fibers. Five traffic grooming policies achieved by adjusting the edge weights of an AG are proposed and evaluated through simulation: maximal electrical grooming (MEG), maximal optical grooming (MOG), maximal SDM grooming (MSG), minimize virtual hops (MVH), and minimize physical hops (MPH). Numeric results show that each traffic grooming policy has its own features. Among different traffic grooming policies, an MPH policy can achieve the lowest bandwidth blocking ratio, MEG can save the most transponders, and MSG can obtain the fewest cores for each request.

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 demonstrate that the CE-RMWPA algorithm can achieve the optimization of RMWPA for reducing cost.

The explosive growth of users’ requirements promotes the development of optical network function virtualization (ONFV) over elastic optical networks (EON). Through optical network virtualization, network services can be provided by sharing physical resources in terms of virtual optical network (VON), which can simplify optical-layer resource management and promote the flexibility of multi-dimensional resource allocation. However, few studies have paid attention to the security of data transmission in VON. Eavesdropping against VON could compromise not just virtualized services, but the whole infrastructure. Quantum key distribution (QKD) integrated with traditional optical network is a promising technology to solve this problem. In this paper, we first demonstrate the concept of VON embedding (VONE) in the EON integrated with QKD. Based on this concept, a dynamic VONE algorithm is proposed to allocate physical network resources to VON requests, which considers not only bandwidth requirements but also key demands. The performance of the proposed VONE algorithm is evaluated via simulation in terms of blocking probability, key resource utilization as well as average path length. Results show that in order to achieve a tradeoff between blocking probability and key resource utilization, the values of adjustment factor and key generation rate should be appropriately set.

A Virtual Network Operator (VNO) is a provider and reseller of network services from other telecommunications suppliers. These network providers are categorized as virtual because they do not own the underlying telecommunication infrastructure. In terms of business operation, VNO can provide customers with personalized services by leasing network infrastructure from traditional network providers. The unique business modes of VNO lead to the emergence of network on demand (NoD) services. The conventional network provisioning involves a series of manual operation and configuration, which leads to high cost in time. Considering the advantages of Software Defined Networking (SDN), this paper proposes a novel NoD service provisioning solution to satisfy the private network need of VNOs. The solution is first verified in the real software defined multi-domain optical networks with multi-vendor OTN equipment. With the proposed solution, NoD service can be deployed via online web portals in near-real time. It reinvents the customer experience and redefines how network services are delivered to customers via an online self-service portal. Ultimately, this means a customer will be able to simply go online, click a few buttons and have new services almost instantaneously.

With the continuous opening of resource acquisition and application, there are a large variety of network hardware appliances deployed as the communication infrastructure. To lunch a new network application always implies to replace the obsolete devices and needs the related space and power to accommodate it, which will increase the energy and capital investment. Network function virtualization1 (NFV) aims to address these problems by consolidating many network equipment onto industry standard elements such as servers, switches and storage. Many types of IT resources have been deployed to run Virtual Network Functions (vNFs), such as virtual switches and routers. Then how to deploy NFV in optical transport networks is a of great importance problem. This paper focuses on this problem, and gives an implementation architecture of NFV-enabled optical transport networks based on Software Defined Optical Networking (SDON) with the procedure of vNFs call and return. Especially, an implementation solution of NFV-enabled optical transport node is designed, and a parallel processing method for NFV-enabled OTN nodes is proposed. To verify the performance of NFV-enabled SDON, the protocol interaction procedures of control function virtualization and node function virtualization are demonstrated on SDON testbed. Finally, the benefits and challenges of the parallel processing method for NFV-enabled OTN nodes are simulated and analyzed.

In this paper, we propose a multi-path fragmentation-aware routing, modulation and spectrum assignment algorithm (RMSA) for advance reservation (AR) and immediate reservation (IR) requests in elastic optical networks. Immediate reservation requests should be provided with service immediately, while advance reservation requests have specific starting times and holding times. As lightpaths are set up and torn down, fragmentation may occur in both spectrum and time domains. To decrease the two-dimensional fragmentation and to solve the problem of resource scarcity, we propose splitting requests into different parts and transferring these parts along one or more paths utilizing sliceable bandwidth variable transponders. We first introduce a model to solve the problem and propose a two-dimensional fragmentation occurrence measurement in spectrum and time domains. Then we propose a multi-path fragmentation-aware RMSA algorithm (MPFA). Simulation results show that MPFA can achieve better performance than existing algorithms in terms of blocking probability and spectrum utilization.

Virtualization is considered to be a promising solution to support various emerging applications. This paper illustrates the problem of virtual mapping from a new perspective, and mainly focuses on survivable mapping of virtual networks and the potential trade-off between spectral resource usage effectiveness and failure resilience level. We design an optimum shared protection mapping (OSPM) scheme in elastic optical networks. A differentiable maximum shared capacity of each frequency slot is defined to more efficiently shared protection resource. In order to satisfy various assessment standards, a metric called ambiguity similitude is defined for the first time to give insight on the optimizing difficulty. Simulation results are presented to compare the outcome of the novel OSPM algorithm with traditional dedicated link protection and maximum shared protection mapping. By synthetic analysis, OSPM outperforms the other two schemes in terms of striking a perfect balance among blocking probability, resources utilization, protective success rate, and spectrum redundancy.

A hierarchical software-defined networking (SDN) control architecture is designed for multi-domain optical networks with the Open Daylight (ODL) controller. The OpenFlow-based Control Virtual Network Interface (CVNI) protocol is deployed between the network orchestrator and the domain controllers. Then, a dynamic bandwidth on demand (BoD) provisioning solution is proposed based on time scheduling in software-defined multi-domain optical networks (SD-MDON). Shared Risk Link Groups (SRLG)-disjoint routing schemes are adopted to separate each tenant for reliability. The SD-MDON testbed is built based on the proposed hierarchical control architecture. Then the proposed time scheduling-based BoD (Ts-BoD) solution is experimentally demonstrated on the testbed. The performance of the Ts-BoD solution is evaluated with respect to blocking probability, resource utilization, and lightpath setup latency.

Optical network virtualization has been studied as a promising technique for optical network resources provisioning. In the virtualization context of Elastic Optical Network (EON), Virtual Optical Network Embedding (VONE) is investigated as a key issue for allocating spectrum resources to VON requests. This paper discusses the continuity constraint for the VONE problem in EONs, and presents three continuity-aware spectrum allocation schemes according to strict and relaxed continuity constraints. We have demonstrated the proposed schemes on emulated testbed to verify the feasibility of composing VON with discontiguous spectrum resources. Additionally, the performances of the proposed schemes are compared via simulation in terms of blocking probability, spectrum resource utilization and discontinuity degree.

The white-box optical ecosystem is considered as the future trend in transport networks, which includes the openness in both software and hardware. The openness in hardware decomposes the equipment into multiple independent components to reduce costs. And the openness in software including general YANG models make all components controllable, which enables fast innovation in the control plane of software-defined networking (SDN). In this paper, an open line architecture (OLA) is proposed to implement the openness and disaggregation to enable white-box optical ecosystem. OLA defines a transport application interface (TAPI) to provide a flexible control of the open line system. To build the physical network, OLA uses the optical equipment developed by different manufacturers that follows specific YANG specifications. And in the control plane, OLA develops a series of drivers and applications to control the calculation, creation, and deletion of optical connectivity service. Finally, the paper shows OLA in use as part of a testbed, which demonstrates the feasibility of building networks consisting of both open and disaggregated hardware.

Alarm prediction in optical networks focuses on forecasting network failure from the state of equipment and links. The existing prediction methods usually rely on large amounts of data, while centralizing all processes in the network controller or management system may increase the system burden. In this paper, a novel method is proposed in self-optimized optical networks (SOON) to implement alarm classification prediction based on cross-layer artificial intelligence (AI) architecture. We adopts alarm risk assessment and data augmentation with synthetic minority oversampling technique (SMOTE). As a distributed system, cross-layer AI completes decomposed functions by using interactions between different AI engines. With the help of the controller system, functions can be executed in order. The amount of data required for prediction is far less than other methods. The validity of the method is proved using the collected data from a commercial synchronous digital hierarchy (SDH) network. Experimental results show that promising precision (95%) can be achieved in predicting the optical equipment alarms.

Because of the realization of physical layer security, the Quantum Stream Cipher (QSC) is getting more and more attention. However, the error rate of each bit of ciphertexts is different from 0.5 for Eve in QSC. This drawback provides Eve with an opportunity to break QSC system possibly through some attacks, such as fast correlation attacks. Thus, to increase the bit error rate of ciphertexts in the higher bit positions to cope with this kind of attacks, this paper proposes a ciphertext mapping method based on Bitwise NOT Operation (BNO). According to parity of bases, BNO-based mapping performs bitwise NOT operation for some bit positions of ciphertext to expand the difference between adjacent bit positions of ciphertexts in QSC. Besides, BNO-based QSC can be directly employed in multi-bit plaintext mapping in QSC for different modulation formats, such as PSK/QSC and QAM/QSC. The security and transmission performance of QSC based on BNO are mainly investigated with different intensity ASE noises and the number of bases in optical back-to-back simulation. The simulation results demonstrate that bit error rate in each bit position of ciphertext is close to 0.5 by BNO method in QSC. Thus, BNO method can expand the impact of noise on the higher bit positions of ciphertext. In addition, BNO method has little influence on transmission performance of receiver in QSC system.

Flexible grid has emerged as an evolutionary technology to satisfy the ever increasing demand for higher spectrum efficiency and operational flexibility. To optimize the spectrum resource utilization, this paper introduces the concept of Spectrum Engineering in flex-grid optical networks. The sliceable optical transponder has been proposed to offload IP traffic to the optical layer and reduce the number of IP router ports and transponders. We discuss the impact of sliceable transponder in traffic grooming and propose several traffic-grooming schemes with Spectrum Engineering (TG-SE). Our results show that there is a tradeoff among different traffic grooming policies, which should be adopted based on the network operator’s objectives. The proposed traffic grooming with Spectrum Engineering schemes can reduce OPEX as well as increase spectrum efficiency by efficiently utilizing the bandwidth variability and capability of sliceable optical transponders.

The end-to-end tunability is important to provision elastic channel for the burst traffic of data center optical networks. Then, how to complete the end-to-end tunability based on elastic optical networks? Software defined networking (SDN) based end-to-end tunability solution is proposed for software defined data center optical networks, and the protocol extension and implementation procedure are designed accordingly. For the first time, the flexible grid all optical networks with Tbps end-to-end tunable transport and switch system have been online demonstrated for data center interconnection, which are controlled by OpenDayLight (ODL) based controller. The performance of the end-to-end tunable transport and switch system has been evaluated with wavelength number tuning, bit rate tuning, and transmit power tuning procedure.

With the rapid growth of data center services, the elastic optical network is a very promising networking architecture to interconnect data centers because it can elastically allocate spectrum tailored for various bandwidth requirements. In case of a link failure, to ensure a high-level quality of service (QoS) for user request after the failure becomes a research focus. In light of it, in this paper, we propose and experimentally demonstrate multipath protection for data center services in OpenFlow-based software defined elastic optical network testbed aiming at improving network reliability. We first propose an OpenFlow-based software defined elastic optical network architecture for data center service protection. Then, based on the proposed architecture, multipath protection scheme is figured based on the importance level of the service. To implement the proposed scheme in the architecture, OpenFlow protocol is extended to support multipath protection in elastic optical network. The performance of our proposed multipath protection scheme is evaluated by means of experiment on our OpenFlow-based testbed. The feasibility of our proposed scheme is also demonstrated in software defined elastic optical networks.

The elastic optical networks can elastically allocate spectrum tailored for various bandwidth requirements. In addition, different virtual optical networks (VONs) formed by different applications or service providers need to be embedded on the common physical optical network, it brings virtual optical network embedding (VONE) problem. There is no precise standard to measure the survivability of VON from the failure probability view and take minimum VON failure probability as an objective in a VONE problem. In this paper, we investigate a survivable VONE problem from a new perspective. Considering probabilistic physical network-element failures, a novel metric, named virtual optical network failure probability (VON-FP), is introduced to evaluate the survivability of VONs in elastic optical networks. Moreover, a failure-probability-aware virtual optical network embedding (FPA-VONE) algorithm is proposed to deploy VONs on the physical network elements with small failure probability, and finally to decrease the VON-FP and enhance the spectrum utilization effectively.

Due to the performance guarantee of low delay, huge bandwidth and high reliability at a low cost, IP over Flexi-Grid optical network is a very promising networking architecture applied to the interconnection of geographically distributed data centers. It can enable efficient resource utilization and support heterogeneous bandwidth demands in cost-effective, highly-available and energy-effective manner. In case of edge Flexi-Grid optical network node failure, to ensure a high-level quality of service (QoS) for user request after the failure becomes a research focus. In this paper, we propose a novel service-aware resources integrated resilience (SA-RIR) scheme for data center services in software defined data center networking architecture based on IP over Flexi-Grid optical networks. Different from previous works which restore the services just exploiting the optical stratum, the proposed scheme provides the resilience using the multiple stratums resources in case of the edge optical node failure. We quantitatively evaluate the feasibility and performances through the simulation under heavy traffic load scenario in terms of path blocking probability, path resilience latency and resource occupation rate with different failure rates. Simulation results show that, the SA-RIR scheme can enable joint optimization of IP network, Flexi-Grid optical network and data center application stratum resources, and enhance the data center service resilience responsiveness to the dynamic end-to-end demands.

This paper focuses on random dual-link failure protection in multi-dimensional node based optical networks. The scenarios of dual-link failure are divided into different types in terms of time and space. And then, the model of pre-configured prism (p-Prism) is built by several pillars and two cycles as the top and bottom to deal with simultaneous dual-link failure. In-depth theoretical analysis is made that p-Prism employs less protection links than p-Cycle. Based on the theory, an efficient integer linear program (ILP) for p-Prism design is formulated, whose objective is to minimize the total protection links. Two protection resource reservation schemes are proposed for different quality of protection requirement. Planar protection routing algorithm (PPRA) on p-Prism is introduced to recover the two failed links. Numeric results show that each of the two schemes can deal with simultaneous dual-link failure. Compared with p-Cycle protection method, p-Prism has better performance at both static and dynamic indexes, such as protection link number, resource redundancy, average protection hops and so on.

Ultrahigh throughout capacity requirement is challenging the current optical switching nodes with the fast development of data center networks. Pbit/s level all optical switching networks need to be deployed soon, which will cause the high complexity of node architecture. How to control the future network and node equipment together will become a new problem. An enhanced Software Defined Networking (eSDN) control architecture is proposed in the paper, which consists of Provider NOX (P-NOX) and Node NOX (N-NOX). With the cooperation of P-NOX and N-NOX, the flexible control of the entire network can be achieved. All optical switching network testbed has been experimentally demonstrated with efficient control of enhanced Software Defined Networking (eSDN). Pbit/s level all optical switching nodes in the testbed are implemented based on multi-dimensional switching architecture, i.e. multi-level and multi-planar. Due to the space and cost limitation, each optical switching node is only equipped with four input line boxes and four output line boxes respectively. Experimental results are given to verify the performance of our proposed control and switching architecture.

Nowadays, most service providers offer their services and support their applications through federated sets of data centers which need to be interconnected using high-capacity optical networks in intra-datacenter networks. Many datacenter applications in the environment require lower delay and higher availability with the end-to-end guaranteed quality of service. In this paper, we propose a novel time-aware software defined networking (TaSDN) architecture for OpenFlow-based intra-datacenter optical interconnection networks. Based on the proposed architecture, a time-aware service scheduling (TaSS) strategy is introduced to allocate the network and datacenter resources optimally, which considers the datacenter service scheduling with flexible service time and service bandwidth according to the various time sensitivity requirements. The TaSDN can arrange and accommodate the applications with required QoS considering the time factor, and enhance the data center responsiveness to quickly provide for intra-datacenter service demands. The overall feasibility of the proposed architecture is experimentally verified on our testbed with real OpenFlow-enabled tunable optical modules. The performance of TaSS strategy under heavy traffic load scenario is also evaluated based on TaSDN architecture in terms of blocking probability and resource occupation rate.

Dynamic flexible grid optical networks have gained much attention because of the advantages of high spectrum efficiency and flexibility, while the performance analysis will be more complex compared with fixed grid optical networks. An analytical Markov model is first presented in the paper, which can exactly describe the stochastic characteristics of the spectrum allocation in flexible grid optical networks considering both random-fit and first-fit resource assignment policies. We focus on the effect of spectrum contiguous constraint which has not been systematically studied in respect of mathematical modeling, and three major properties of the model are presented and analyzed. The model can expose key performance features and act as the foundation of modeling the Routing and Spectrum Assignment (RSA) problem with diverse topologies. Two heuristic algorithms are also proposed to make it more tractable. Finally, several key parameters, such as blocking probability, resource utilization rate and fragmentation rate are presented and computed, and the corresponding Monte Carlo simulation results match closely with analytical results, which prove the correctness of this mathematical model.

Quantum noise stream cipher (QNSC) is a physical layer encryption technique based on quantum noise. Discrete-fourier-transform spread orthogonal frequency division multiplexing (DFTs-OFDM) is a widely studied technology with excellent transmission performance. As best as we know, the transmission and security performance of QNSC in DFTs-OFDM transmission has not been studied. This paper introduces DFTs-OFDM into the QNSC system to combine the characteristics of both techniques. Simulation results show that PSK-based QNSC (PSK/QNSC) has better transmission and security performance than QAM-based QNSC (QAM/QNSC) under the same constellation size. As the constellation size increases, obtained security can be upgraded. We also investigate the effects of quantization and clipping noise on the performance of DFTs-OFDM based QAM/QNSC system. We experimentally demonstrate a 10-Gbit/s DFTs-OFDM based PSK/QNSC and QAM/QNSC transmission over a single span 200-km fiber link.

In this paper, to decrease the traffic loss caused by multiple link failures, we consider the correlated risk among different connection requests when both the primary and backup paths are routed and assigned spectrum. Therefore, a novel shared-path protection algorithm is developed, named shared-path protection algorithm with correlated risk (SPP_CR), in flexible bandwidth optical networks. Based on the correlated risk, the routing can be diverse and the sharing in backup spectral resource will be restricted by SPP_CR algorithm, then the dropped traffic caused by simultaneous multiple failures between primary and backup path can be efficiently decreased. Simulation results show that, SPP_CR algorithm (i) achieves the higher successful service ratio (SSR) than traditional shared-path protection (SPP), shared-path protection with dynamic load balancing (SPP_DLB) and dedicated path protection (DPP); (ii) makes a better tradeoff in blocking probability, protection ratio (PR), average frequency slots consumed (AFSC) and redundancy ratio (RR) than SPP, SPP_DLB and DPP algorithms.

In this paper, we investigate network performance of multi-link failure restoration in spectrum-elastic optical path networks (SLICE). To efficiently restore traffic under multi-link failures, a novel survivable algorithm, named dynamic load balancing shared-path protection (DLBSPP), is proposed to compute primary and link-disjoint shared backup paths. The DLBSPP algorithm employs first fit (FF) and random fit (RF) schemes to search and assign the available spectrum resource. Traffic-aware restoration (TAR) mechanism is adopted in the DLBSPP algorithm to compute new routes for carrying the traffic affected by the multi-link failures and then the multi-link failures can be efficiently restored. Simulation results show that, compared with the conventional shared-path protection (SPP) algorithm, the DLBSPP algorithm achieves lower blocking probability (BP), better spectrum utilization ratio (SUR), more reasonable average hop (AH) and higher failure restoration ratio (FRR). Thus, the proposed DLBSPP algorithm has much higher spectrum efficiency and much better survivability than SPP algorithm.

The real-time scheduling and routing in dynamic transparent optical networks requires fast and accurate evaluation of transmission penalty caused by nonlinear kerr effects with different dispersion maps. However, the conventional method using nonlinear phase shift can only be applied to assess the nonlinear penalty with optimized dispersion maps. In this paper, we introduce pulse broadening factor into the approach and propose a novel method to accurately evaluate nonlinear penalty and numerically investigate the feasibility of our novel method in 40-Gb/s Return-to-Zero Differential Quadrature Phase-Shift Keying (RZ-DQPSK) systems. Simulation results show that our approach can achieve good evaluation performance even with non-optimized dispersion maps.