All-optical Networks Research Articles

An offline scheme for reducing cost of protection in all-optical WDM mesh networks with fast recovery

ABSTRACTIn Optical WDM networks, a single fiber carries enormous amount of data and consequently designing schemes to prevent the user traffic from disruption and techniques to recover from failures still remains an important area of research. In this paper we address the problem of protecting all-optical WDM mesh networks from single link failure. We propose an offline protection scheme that is not only cost-efficient in terms of network resource consumption but can also provide quick recovery from a link failure. In our scheme, backup paths are combined to reduce cost of protection and to facilitate fast recovery from a failure. We address a critical issue related to selection of backup paths to be combined, which was not addressed earlier. Instead of choosing backup paths for connection requests arbitrary as done in an existing scheme, our scheme is designed to select backup paths in a way that they are suitable for combination and can maximize resource saving as well. We first provide an Integer Linear Program for the problem, and then propose a heuristic eStreams that can provide near optimal solution in polynomial time. Performance comparisons with some well-known schemes show that our protection scheme is definitely an improvement in terms resource conservation while ensuring fast recovery from a link failure.The figure shows how a primary (working) path is protected with the help of a link-disjoint backup path in WDM optical networks. A primary path is used to carry traffic under normal fault free condition. In the event of a link fault (fiber-cut) the traffic is switched over to the backup path.

An improved approximate network blocking probability model for all-optical WDM Networks with heterogeneous link capacities

Abstract Currently, analytical models are used to compute approximate blocking probabilities in opaque and all-optical WDM networks with the homogeneous link capacities. Existing analytical models can also be extended to opaque WDM networking with heterogeneous link capacities due to the wavelength conversion at each switch node. However, existing analytical models cannot be utilized for all-optical WDM networking with heterogeneous structure of link capacities due to the wavelength continuity constraint and unequal numbers of wavelength channels on different links. In this work, a mathematical model is extended for computing approximate network blocking probabilities in heterogeneous all-optical WDM networks in which the path blocking is dominated by the link along the path with fewer number of wavelength channels. A wavelength assignment scheme is also proposed for dynamic traffic, termed as last-fit-first wavelength assignment, in which a wavelength channel with maximum index is assigned first to a lightpath request. Due to heterogeneous structure of link capacities and the wavelength continuity constraint, the wavelength channels with maximum indexes are utilized for minimum hop routes. Similarly, the wavelength channels with minimum indexes are utilized for multi-hop routes between source and destination pairs. The proposed scheme has lower blocking probability values compared to the existing heuristic for wavelength assignments. Finally, numerical results are computed in different network scenarios which are approximately equal to values obtained from simulations.

Greedy Constructions of Optical Queues With a Limited Number of Recirculations

One of the main problems in all-optical packetswitched networks is the lack of optical buffers, and currently the only known feasible technology for the constructions of optical buffers is to use optical crossbar Switches and fiber Delay Lines (SDLs). In this paper, we consider SDL constructions of optical queues with a limited number of recirculations through the optical switches and the fiber delay lines. Such a problem arises from practical feasibility considerations, such as crosstalk, power loss, amplified spontaneous emission from the Erbium doped fiber amplifiers, and the pattern effect of the optical switches. We first transform the design of the fiber delays in such SDL constructions into an equivalent integer representation problem. Specifically, given 1 ≤ k ≤ M, we seek for an M-sequence d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</sub> = (d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> , d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , ..., d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</sub> ) of positive integers to maximize the number of consecutive integers (starting from 0) that can be represented by the C-transform (a generalization of the well-known binary representation) with respect to d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</sub> such that there are at most k 1-entries in their C-transforms. Then, we propose a class of greedy constructions of d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</sub> , in which d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> , d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , ..., d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</sub> are obtained recursively in a greedy manner so that the number of representable consecutive integers by using d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> , d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , . .., d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i</sub> is larger than that by using d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> , d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , . .., d <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">i-1</sub> for all i. Finally, we show that every optimal construction (in the sense of maximizing the number of representable consecutive integers) must be a greedy construction. As a result, the complexity of searching for an optimal construction can be greatly reduced from exponential time to polynomial time by only considering the greedy constructions rather than performing an exhaustive search. The solution of such an integer representation problem can be applied to the constructions of optical 2-to-1 FIFO multiplexers with a limited number of recirculations. Similar results can be obtained for the constructions of optical linear compressors/decompressors with a limited number of recirculations.

Active Control of Slow Light in a Gain-Assisted Plasmon-Induced Transparency Structure

Plasmon-induced transparency (PIT) in a compact plasmonic resonator structure, which consists of a metal– dielectric–metal waveguide with an aperture-coupled square cavity and a slot resonator, is investigated theoretically and numerically. We find the transparency window and the delay of slow light in this structure can be controlled at a fixed wavelength by carefully adjusting the geometrical parameters of the aperture-coupled square cavity. By introducing gain medium into the slot resonator, the transmittance and the group index in transparency window both are dramatically enhanced with optically pumping the medium, and the group delay time can reach to 0.93 ps. In addition, triple PIT effects are also achieved by adding another aperture-coupled cavity and slot cavity, and corresponding slow light also can be dynamically tuned. This study paves a new route toward the realization of highly integrated all-optical circuits and networks, especially for ultrafast switches, optical buffers, lasers, and nanosensors.

An online cost-efficient protection scheme for quick recovery in all-optical WDM mesh networks

Since a single fiber carries a huge amount of data in optical WDM networks, a fiber cut even for a brief period is a very serious event. Designing schemes to prevent disruption of user traffic and recovery techniques from failures is thus an important area of research. Since a single fiber cut is the most common type of fault, in this paper we address the problem of protecting all-optical WDM mesh networks from single link failure. Our proposed online protection scheme is an improvement over an existing approach and is not only cost-efficient in terms of network resource consumption but can also provide quick recovery from a link failure. We first provide an ILP formulation for the problem and then propose a heuristic solution iStreams that can provide near-optimal solution in polynomial time. Performance comparisons with some well-known schemes of protection show that our heuristic algorithm can be a better choice for conserving resource while providing quick recovery from a link failure.

Adaptive Policies for Scheduling With Reconfiguration Delay: An End-to-End Solution for All-Optical Data Centers

All-optical switching networks have been considered a promising candidate for the next generation data center networks thanks to its scalability in data bandwidth and power efficiency. However, the bufferless nature and the nonzero recon- figuration delay of optical switches remain great challenges in deploying all-optical networks. This paper considers the end-to- end scheduling for all-optical data center networks with no in- network buffer and nonzero reconfiguration delay. A framework is proposed to deal with the nonzero reconfiguration delay. The proposed approach constructs an adaptive variant of any given scheduling policy. It is shown that if a scheduling policy guarantees its schedules to have schedule weights close to the MaxWeight schedule (and thus is throughput optimal in the zero reconfiguration regime), then the throughput optimality is inherited by its adaptive variant (in any nonzero reconfiguration delay regime). As a corollary, a class of adaptive variants of the well known MaxWeight policy is shown to achieve throughput optimality without prior knowledge of the traffic load. Further- more, through numerical simulations, the simplest such policy, namely the Adaptive MaxWeight (AMW), is shown to exhibit better delay performance than all prior work.

Metropolitan Area Network Architecture for Optical Flow Switching

In this work, we provide design concepts of efficient physical and lightpath topology architectures for a LAN/MAN all-optical network that support Optical Flow Switching. We found good architectures are coupled intimately with media access control protocol designs and must be optimized jointly. Two architectures that represent extreme cases were examined: Quasi-Static Architecture and Dynamic Per Flow Routing Architecture. The performance and costs are compared to provide an economical architecture design.

Bidirectional all-optical switches based on highly nonlinear optical fibers

All-optical switches have become one of the research focuses of nonlinear optics due to their fast switching speed. They have been applied in such fields as ultrafast optics, all-optical communication and all-optical networks. In this paper, based on symbolic computation, bidirectional all-optical switches are presented using analytic two-soliton solutions. Various types of soliton interactions are analyzed through choosing the different parameters of high-order dispersion and nonlinearity. Results indicate that bidirectional all-optical switches can be effectively achieved using highly nonlinear optical fibers.

All-optical XOR and OR by Mach-Zehnder Interferometer engineered photonic crystal fibers

In this paper, we present a numerical investigation of all-optical logic gates based on a Mach-Zehnder Interferometer (MZI) configuration of micro structured fibers, also known as photonic crystal fibers (PCF) under optical OOK (on-off keying). We determine several relevant quantities to characterize the system performance, such as transmission and extinction ratio as a function of the nonlinearity profile (β) added to one of the Mach-Zehnder Interferometer (MZI) arms. High-order effects such as third-order dispersion, intrapulse Raman scattering and self-steepening were included in the generalized nonlinear Schrödinger equation describing the pulse propagation. For this study, we used an optical pulse with a shape of hyperbolic secant of 100fs (femtosecond). A pumped laser with three power values was simulated. With critical power Pc=103.5kW (P=Pc), below the critical power P=90kW (P<Pc) and above the critical power P=110kW (P>Pc). We added a nonlinearity profile in one of the Mach-Zehnder Interferometer (MZI) arms. Nonlinearity profiles were expressed in terms of the parameter β. We studied three different profiles: constant, increasing and decreasing. Our results show that the proposed device can be used to obtain all-optical OR and XOR logic gates as well as logic functions A and A.B¯. The OR logic gate was the one which achieved the greatest FOMELG (Figure of Merit of Logic Gates) when using increasing profile with critical power (P0=103.5kW) for β=1.05 and FOMELG=15.68dB. The XOR logic gate presented the greatest FOMELG=7.75dB when using the decreasing profile with power below the critical (P0=90kW) for β=1.44. These results provide support for applications in all-optical networks.

Photonic transistor and router using a single quantum-dot-confined spin in a single-sided optical microcavity

The future Internet is very likely the mixture of all-optical Internet with low power consumption and quantum Internet with absolute security guaranteed by the laws of quantum mechanics. Photons would be used for processing, routing and com-munication of data, and photonic transistor using a weak light to control a strong light is the core component as an optical analogue to the electronic transistor that forms the basis of modern electronics. In sharp contrast to previous all-optical tran-sistors which are all based on optical nonlinearities, here I introduce a novel design for a high-gain and high-speed (up to terahertz) photonic transistor and its counterpart in the quantum limit, i.e., single-photon transistor based on a linear optical effect: giant Faraday rotation induced by a single electronic spin in a single-sided optical microcavity. A single-photon or classical optical pulse as the gate sets the spin state via projective measurement and controls the polarization of a strong light to open/block the photonic channel. Due to the duality as quantum gate for quantum information processing and transistor for optical information processing, this versatile spin-cavity quantum transistor provides a solid-state platform ideal for all-optical networks and quantum networks.

Dark Solitons and Grey Solitons in Waveguide Arrays with Long-Range Linear Coupling Effects

In J. Phys. Soc. Jpn. 83, 034404 (2014), we designed a scheme of waveguide arrays with long-range linear coupling effects and studied the bright solitons in this system. In this paper, we further study the dynamics of dark and grey solitons in such waveguide arrays. The numerical simulations show that the stabilities of dark solitons and grey solitons depend on the normalized decay length and the scaled input power. The width of dark solitons and the grey level of grey solitons are studied. Our results may contribute to the understanding of discrete solitons in long-range linear coupling waveguide arrays, and may have potential applications in optical communications and all-optical networks.

Elastic All-Optical Networks: A New Paradigm Enabled by the Physical Layer. How to Optimize Network Performances?

A new era for optical networks has been started by the development of transceivers based on digital signal processing and operating multilevel modulation formats with coherent and equalized receivers, enabling uncompensated optical links and dynamic transparent wavelength routing in nodes. Connectivity matrices at the physical layer have changed from sparse and static to full and elastic . Therefore, to fully exploit network potentialities and to implement the elasticity paradigm requested by the forecasts of worldwide Internet traffic evolution, the orchestration of logical and physical layer has become a firm requirement. We propose the statistical network assessment process (SNAP) as a method to explore potentialities of physical layer independently of specific traffic allocation. We apply SNAP to a German and to a Pan-EU network topology, first deriving the average bit-rate per lightpath given an any-to-any connectivity matrix—a static metric—in order to compare merits of three typical fiber types and to evaluate benefits of time-division hybrid modulation formats. Then, assuming physical layer characteristics are set, we perform a SNAP investigation versus progressive network loading evaluating the blocking probability versus total allocated traffic—a dynamic metric—comparing merits of different size in traffic grooming operating together with multi- or fixed-rate transceivers. We also show how the progressive loading analysis can be used to address selected physical layer upgrades. As an example, we investigate possible upgrades to hybrid Raman/Erbium fiber amplification on selected links, then displaying quantitative benefits in terms of enabled excess traffic at a given blocking probability.

Flexible bandwidth assignment with application to optical networks

We introduce two scheduling problems, the flexible bandwidth allocation problem ( $$\textsc {FBAP}$$ ) and the flexible storage allocation problem ( $$\textsc {FSAP}$$ ). In both problems, we have an available resource, and a set of requests, each consists of a minimum and a maximum resource requirement, for the duration of its execution, as well as a profit accrued per allocated unit of the resource. In $$\textsc {FBAP}$$ , the goal is to assign the available resource to a feasible subset of requests, such that the total profit is maximized, while in $$\textsc {FSAP}$$ we also require that each satisfied request is given a contiguous portion of the resource. Our problems generalize the classic bandwidth allocation problem (BAP) and storage allocation problem (SAP) and are therefore $$\text {NP-hard}$$ . Our main results are a 3-approximation algorithm for $$\textsc {FBAP}$$ and a $$(3+\epsilon )$$ -approximation algorithm for $$\textsc {FSAP}$$ , for any fixed $$\epsilon >0 $$ . These algorithms make nonstandard use of the local ratio technique. Furthermore, we present a $$(2+\epsilon )$$ -approximation algorithm for $$\textsc {SAP}$$ , for any fixed $$\epsilon >0 $$ , thus improving the best known ratio of $$\frac{2e-1}{e-1} + \epsilon $$ . Our study is motivated also by critical resource allocation problems arising in all-optical networks.

JMAWR: joint optimization of monitoring trail allocation and wavelength routing with limited monitoring resources

In all-optical networks, monitoring trail (m-trail) has long been proposed as an effective way for link failure localization. Previous works tried to minimize the number of used m-trails for localizing network-wide single link failures, and they all supposed that the monitoring resources were enough. However, failures are rare events and the traffic demand is increasing rapidly. The dedicated wavelengths for m-trails cannot be used to transmit data traffic, and some traffic demand may not be served during the peak period. Considering the operators prefer to serve customers’ demand as much as possible, if the resources allocated for m-trails are limited, more traffic will be carried. In this paper, we focus on the scenario where there are not enough resources for allocating m-trails. In this scenario, as only part of single link failures can be unambiguously localized, we aim to monitor the most valuable links, which carry more traffic demand, and minimize the maximum number of used wavelengths for traffic demand on the links which cannot be unambiguously localized. As we can also control the wavelength routing for traffic demand, we try to jointly optimize the m-trail allocation and wavelength routing. We first formulate this joint optimization problem as a mathematical model and present concrete analyses on this model. According to these analyses, a joint m-trail allocation and wavelength routing (JMAWR) heuristic algorithm is proposed based on graph-constrained group testing. Simulation results show that JMAWR outperforms the state-of-the-art m-trail allocation algorithm by up to 88.46% improvement in terms of maximum number of used wavelengths for traffic demand on links which cannot be unambiguously localized.

Nonlinear Silicon Photonic Signal Processing Devices for Future Optical Networks

In this paper, we present a review on silicon-based nonlinear devices for all optical nonlinear processing of complex telecommunication signals. We discuss some recent developments achieved by our research group, through extensive collaborations with academic partners across Europe, on optical signal processing using silicon-germanium and amorphous silicon based waveguides as well as novel materials such as silicon rich silicon nitride and tantalum pentoxide. We review the performance of four wave mixing wavelength conversion applied on complex signals such as Differential Phase Shift Keying (DPSK), Quadrature Phase Shift Keying (QPSK), 16-Quadrature Amplitude Modulation (QAM) and 64-QAM that dramatically enhance the telecom signal spectral efficiency, paving the way to next generation terabit all-optical networks.

High Speed VCSEL Transmission at 1310 nm and 1550 nm Transmission Wavelengths

Vertical cavity surface emitting lasers (VCSELs) operating at 1310 nm and 1550 nm are very promising sources for access and interconnections in telecommunication systems due to their technologically attractive properties such as low threshold currents and narrow spectral linewidth due to single mode operation. VCSELs are also being rapidly commercialized for single-mode fibre metropolitan area and wide area network applications. All these advantages leads to cost-effective wavelength-tunable lasers, which are essential for the future intelligent, all-optical networks. Direct modulation (DM) of VCSEL with separate optical and current apertures enables high modulation bandwidth operating at single mode at low current density. However, dispersion and attenuation is a major hurdle to VCSELs transmission at bit rate of 10 Gb/s and above. In this study, a 1310 and 1550 nm VCSELs were directly modulated with 10 Gb/s NRZ PRBS 2⁷-1 and transmitted over 25 km ITU. T G.652 and ITU. T G.655 fibres and optimized for metro-access distances. A low dispersion penalty was realized when a 1550 nm VCSEL was used on a G.655 fibre and when a 1310 nm source was transmitted over a G.652 fibre. The transmission system has been analyzed on the basis of different parameters, which are (Bit error rate) BER, Quality (Q) factor and Output power.

Virtual-Pod-Assisted Routing and Resource Assignment in Elastic All-Optical Intra-Datacenter Networks

The service requests of intra-datacenter networks (intra-DCNs) are different from the traffic demands of traditional transport networks in the following features. First, the latter is typically generated between dedicated node pairs that only require sufficient transmission bandwidth. Intra-DCN service requests, in contrast, require IT resources, such as computational, memory and storage resources, in addition to the transmission bandwidth. Second, for a given intra-DCN service request, any intra-DCN node that can provide the required IT resources can serve as a destination node (i.e., anycast). Thus, this type of network poses an important research problem of routing and spectrum/IT resource assignment (RSIA). To support these features, we first develop an integer linear programming (ILP) model to address the static RSIA problem, and then to propose efficient heuristic algorithms to address the dynamic RSIA issues, subject to the intra-DCNs’ limited network resources. The results of the proposed ILP model and heuristic algorithms are compared with the traditional network models and algorithms. It is found that the proposed ILP model and heuristic algorithms perform much better than the traditional approaches in terms of using intra-DCN network resources and reducing the service-request blocking probability.

Study of Qos Performance in Optical Burst Switched Networks (OBS)

One of the main challengers of the future Internet is to ensure QoS for various types of traffic characteristics with differentiated service requirements. It has been highlighted that OBS can provide high bandwidth data transmission in alloptical Internet network. However, the provisioning of QoS in OBS network is still an issue. The focused of this study is to develop QoS provisioning mechanism at the ingress and core node of OBS network. The proposed QoS provisioning ensures that the differentiated traffic is able to achieve their respective demands. This study proposed a DiffServ-aware ingress node with priority queueing (PQ) and burst assembly mechanisms. In addition, a core node with contention resolution scheme using FDL_WA_WPremp is developed as part of the integration of the proposed OBS network.

All-Optical Virtual Private Network in OFDM-PON Using Microwave Photonic Filter

We propose and demonstrate a novel all-optical virtual private network (VPN) using a microwave photonic filter, which enables inter-communications among optical network units in a passive optical network system. In our scheme, an optical coupler based recirculating delay line is used at optical line terminal as an optical subsystem to implement a microwave photonic-bandpass filter (MP-BPF). The periodic passbands of an MP-BPF are used to transmit VPN signal, whereas stopbands are used for conventional upstream transmission. The proposed system has two critical issues, optical phase-induced intensity noise in the MP-BPF and Rayleigh back-scattering interference by a single-fiber loop back link. To overcome the issues, an RF clipping tone based spectrum-broadening technique is applied to uplink transmitter. The proposed all-optical VPN system is tolerant to wavelength of VPN optical carrier, and enables multi-VPN data transmission using multi-passbands of MP-BPF.

Tuning of whispering gallery modes in a magnetic-fluid-infiltrated silica capillary based on lateral pumping scheme

An all-optical tuning method of whispering gallery modes (WGMs) in a silica capillary based on lateral pumping scheme has been proposed and experimentally demonstrated by exploiting the photo-thermal effect of magnetic fluids (MFs) infiltrated into a micro-capillary. The WGMs are coupled from a tapered fiber perpendicular to the silica capillary. Experimental results indicate that the microresonator integrated with MFs shows a Q-factor of 1.2867 × 104 and its optical tunability reaches 0.0382 nm/(mW · mm−2) under 532 nm laser illumination. Compared with the one infiltrated with pure water, our proposed capillary shows an optical tuning sensitivity increase of about 4270 times. The experimental results on the WGM resonance wavelength sensitivity for the capillaries with different diameters are in accordance with our simulation outcome using radially dependent heat conducting equation. Further experimental studies indicate that the proposed microresonator possesses a good spectral reversibility. Moreover, the dynamic response experiment shows that the rise and fall time of this microresonator is about 231 ms and 255 ms, respectively. The above intriguing features make the proposed WGM resonator a promising candidate for potential applications in optical filtering, microfluidic sensing, and signal processing as well as reconfigurable devices for future all-optical networks.