Multiwavelength Optical Networks Research Articles

Scalable node-disjoint and edge-disjoint multiwavelength routing.

Probabilistic message-passing algorithms are developed for routing transmissions in multiwavelength optical communication networks, under node- and edge-disjoint routing constraints and for various objective functions. Global routing optimization is a hard computational task on its own but is made much more difficult under the node- and edge-disjoint constraints and in the presence of multiple wavelengths, a problem which dominates routing efficiency in real optical communication networks that carry most of the world's internet traffic. The scalable principled method we have developed is exact on trees but provides good approximate solutions on locally treelike graphs. It accommodates a variety of objective functions that correspond to low latency, load balancing, and consolidation of routes and can be easily extended to include heterogeneous signal-to-noise values on edges and a restriction on the available wavelengths per edge. It can be used for routing and managing transmissions on existing topologies as well as for designing and modifying optical communication networks. Additionally, it provides the tool for settling an open and much-debated question on the merit of wavelength-switching nodes and the added capabilities they provide. The methods have been tested on generated networks such as random-regular, Erdős Rényi, and power-law graphs, as well as on optical communication networks in the United Kingdom and United States. They show excellent performance with respect to existing methodology on small networks and have been scaled up to network sizes that are beyond the reach of most existing algorithms.

Toward transformable photonics: Reversible deforming soft cavities, controlling their resonance split and directional emission

We report on reversible and continuously deformable soft micro-resonators and the control of their resonance split and directional emission. Assisted by computerized holographic-tweezers, functioning as an optical deformer of our device, we gradually deform the shape and change the functionality of a droplet whispering-gallery cavity. For example, we continuously deform hexagonal cavities to rectangular ones and demonstrate switching to directionally emitting mode-of-operation, or splitting a resonant mode to a 10-GHz separated doublet. A continuous trend of improving spatial light modulators and tweezers suggests that our method is scalable and can control the shape and functionality of many individual devices. We also demonstrate optional solidification, proving the feasibility of transformer-enabled applications, including in printing optical circuits and multiwavelength optical networks.

Chirped fiber grating and specialty fiber based multiwavelength optical beamforming network for 1X8 phased array antenna in S-band

In this paper, theoretical and experimental analysis has been done for the beam transmission of 2.2 GHz RF signal by 1X8 linear phased array antenna fabricated in S-band. The proposed architecture is based on true time delay optical beam forming network which gives squint free beam steering of RF signal. The optical beam forming network is based on chirp fiber Bragg grating (CFBG) and multiple lengths of highly dispersive specialty fiber element. Here, double sideband modulation technique of multiple wavelengths are adopted which explore the reflection property of CFBG with various chirp bandwidth. We measured the reflectivity and time delay response of CFBG, and dispersive fiber elements with theoretical analysis which is verified by experimental results. Theoretical and experimental measurements for the relative time delay was used to investigate the beam radiation pattern of 1X8 phased array antenna through simulation results. Wide range of beam steering ranges 3.5° to 18° have been achieved when specialty fiber of −100 ps/nm km dispersion coefficient was introduced.

5D data iteration in a multi-wavelength OFDM-PON using the hyperchaotic system.

In this Letter, a novel five-dimensional (5D) data-iteration-based encryption model is proposed at physical layer for multi-wavelength optical frequency division multiplexing passive optical network (OFDM-PON) by using a hyperchaotic system. The proposed scheme can generate five chaotic sequences at a time. The sensitivity of 10-18 can be achieved, along with a key space of 1095. In addition, we use a multi-wavelength channel to transmit the information, and the optical network unit can freely choose the wavelength. The probability shaping technology has greatly improved the bit error rate performance. A 16Gb/s/λ data is successfully transmitted across 25 km standard single-mode fiber in the experimental verifications. Therefore, it will have a positive impact in the future security optical network.

Joint Allocation of Radio and Fronthaul Resources in Multi-Wavelength-Enabled C-RAN Based on Reinforcement Learning

Cloud radio access network (C-RAN) is a key technology for the new-generation mobile network (5G). Multi-wavelength passive optical networks (PONs) such as wavelength division multiplexing (WDM) and time wavelength division multiplexing (TWDM) PONs are outstanding solutions for providing a sufficient bandwidth to support mobile fronthaul in C-RAN-based 5G architecture. In this paper, a joint allocation framework for multi-wavelength PONs fronthaul uplink resources and C-RAN radio interface uplink resources is presented. From the principle that the uplink resource allocation in mobile networks is an NP-hard optimization problem, this paper proposes a novel uplink scheduling algorithm based on reinforcement learning (RL). The performance of the algorithm is evaluated with numerical simulations and compared with two other algorithms from the literature; namely genetic algorithm (GA) and tabu search (TS) algorithm. The simulation results show that the new algorithm achieves higher system throughput, faster convergence and lower scheduling latency compared to the two other algorithms. Also, show that RL-based adaptive allocation of fronthaul transport block size based on actual radio resource block capacity can significantly reduce the capacity required on fronthaul link and decrease the total end to end uplink scheduling latency compared to the static allocation method.

Performance analysis and optimization of wavelength routed (WR) and wavelength selected (WS) hybrid optical distributed network (ODN) for next generation passive optical network stage 2 (NG-PON2)

Next-generation passive optical network stage 2 (NG-PON2) supports the wavelength routed optical distributed network (WR-ODN), power splitter optical distributed network or wavelength-selected optical distributed network (WS-ODN) and hybrid of both the architecture configuration. NG-PON2 is world’s first multi-wavelength passive optical network (PON) standard. The fiber dispersion and nonlinearity degrades the performance of NG-PON2 severely. Fiber nonlinearity depends on the optical launch power and fiber reach. This paper focuses on maximizing the network performance and maximizing the number of simultaneous users with error-free performance by optimizing the optical launch power respectively at dynamic reach and differential reach. The optical launch power is optimized to abate the fiber nonlinearity and significantly enhances the performance of NG-PON2 at dynamic fiber reach for Alcatel 6912 Teralight Ultra 1625 commercial fiber specification. Furthermore, precise values of the optimum launch power for the dynamic fiber reach, for different NG-PON2 architecture, under industrial fiber specification is meticulously obtained. It is identified that irrespective of both, WR-ODN and WS-ODN architecture configuration, optimum launch power remains constant. Power budget is calculated for both, maximizing the performance and maximizing the simultaneous number of users at differential reach and dynamic reach of the NG-PON2.

A Single-Star Multi-Ring Structure of Self-Healing Wavelength Division Multiplexing Optical Access Network

A simple single-star multi-ring structure of multi-wavelength optical access network for enlarging network scale and protecting distribution fiber is presented. In this scheme, the ring structure enables optical network units to switch automatically to a protection link when the distribution fiber fails, and a star structure is adopted to weaken the sphere of the distribution fiber failure's influence. The simple combination of these two structures greatly increases the number of subscribers and minimizes costs of network. The network's survivability can also be better than that of a star network or ring network. In addition, it can easily be upgraded from an existing star network, so this article also proposes a method to update the existing star network. The simulation result shows the structure is of good performance.

Joint bandwidth allocation on dedicated and shared wavelengths for QoS support in multi‐wavelength optical access network

Wavelength-division multiplexing (WDM) technology has been recognised as one of the most promising solutions in optical access network. A general ring-based multi-wavelength optical access network based on WDM technology, which can realise triple-play service including point-to-point service and multicast service is introduced in this study. To effectively utilise the network bandwidth resources, the authors propose a joint bandwidth allocation scheme on dedicated and shared wavelengths. The proposed scheme focuses on quality of services (QoSs) support. It is carried out according to the priority queue discipline to support QoS in terms of average packet delay, packet delay variance and throughput. Moreover, with the fair-awareness in the scheduling scheme, the lower priority services can be prevented from starvation and the over-allocation problem can be avoided. The simulation results show that the proposed scheme can reduce average packet delay and packet delay variance for high-priority services to ensure QoS.

Tunable self-seeding Fabry–Pérot laser diode for upstream multiwavelength shared ethernet passive optical network

We present a novel upstream multiwavelength shared ethernet passive optical network architecture, based on a proposed self-seeding Fabry-Perot laser diode (FP-LD) at the optical network unit. The performances of the wavelength and power stability, side-mode suppression ratio, and tuning range for the proposed tunable self-seeding laser module are experimentally investigated. The bit-error-rate measurement is performed with direct modulation on FP-LD of 1.25 Gbps upstream data. The performance benefits from the upstream wavelengths sharing are showed via simulations.

Multi-Wavelength WiMAX–PONs With Overlapping Cells

An access network architecture integrating standard wireless signal formats over multi-wavelength splitter passive optical networks (PONs) based on radio-over-fiber (RoF) technology is demonstrated. Frequency division multiplexing (FDM) is applied to address individual base stations sharing a single wavelength. The extended wavelength band overlay overcomes the need for complex dispersion compensation techniques as it avoids the use of high frequency subcarriers in the FDM window. Also, it achieves enhanced network scalability compared with previously reported converged architectures as well as reduced component cost. Significantly, extended features of wireless networks have been presented through the application of overlapping cells to overcome the wireless spectrum congestion beyond current deployment scenarios and provide resilience for legacy PONs. To evaluate the network transmission characteristics, multiple IEEE802.16d channels, with 70 Mbits/s downstream and 40 Mbits/s upstream data rates, are frequency shifted around the same RF carrier and transmitted on two different wavelengths. The obtained results have demonstrated error vector magnitudes (EVMs) of -31 dB at optical network unit/base-station (ONU/BS) remote antenna inputs and minimum 10-4 bit error rates (BERs) bidirectionally over combined 20 km and faded 330 m overlapping micro-cell circumferences without any error coding or relay techniques. The application of a low-cost long-wavelength vertical cavity surface emitting laser (VCSEL) array in upstream for colorless transmission demonstrated 0.7 dB power penalty to the received worldwide interoperability for microwave access (WiMAX) channels in the optical line terminal (OLT).

一种基于反射型半导体光放大器和迈克逊干涉仪的无色远端节点的设计和分析

A scheme of flexible colorless remote note with reflective semiconductor optical amplifier (RSOA) assisted Michelson interferometer is proposed. This is capable of generating an optical carrier suppressed signal at a specific radio frequency to suppress the penalty brought about by Rayleigh backscattering and reflection in a full-duplex single fiber transmission network. Simulations are conducted, and the validation of the proposal is discussed by observing the penalty eye opening factor. The results are useful for designing cost-effective multi-wavelength passive optical network (PON) or radio-over-fiber (RoF) systems.

A Lagrangean relaxation based near-optimal algorithm for advance lightpath reservation in WDM networks

Advance lightpath reservation is a new research topic for connecting high-speed computer servers in lambda grid applications and for dynamic lightpath provisioning in the future optical internet. In such networks, users make call requests in advance to reserve network resources for communications. The challenge of the problem comes from how to jointly determine call admission control, lightpath routing, and wavelength assignment. In this paper, we propose an efficient Lagrangean relaxation (LGR) approach to resolve advance lightpath reservation for multi-wavelength optical networks. The task is first formulated as a combinatorial optimization problem in which the revenue from accepting call requests is to be maximized. The LGR approach performs constraint relaxation and derives an upper-bound solution index according to a set of Lagrangean multipliers generated through subgradient-based iterations. In parallel, using the generated Lagrangean multipliers, the LGR approach employs a new heuristic algorithm to arrive at a near-optimal solution. By upper bounds, we assess the performance of LGR with respect to solution accuracy. We further draw comparisons between LGR and three heuristic algorithms—Greedy, First Come First Serve, and Deadline First, via experiments over the widely-used NSFNET network. Numerical results demonstrate that LGR outperforms the other three heuristic approaches in gaining more revenue by receiving more call requests.

Bit error rate reduction by power shaping in WDM networks with EDFAs

The trend in multi-wavelength optical networks is toward dynamic route and wavelength assignment to support burst-switching or packet switching. Where erbium-doped optical amplifiers (EDFAs) are used for multi-wavelength amplifications, the time interval between traffic blocks can be long enough to induce EDFA optical power transients created by abrupt changes in the average input power to the EDFAs and can adversely affect the performance of the network. To mitigate the effects of EDFA optical power transients on optical networks, a method based on power shaping where heads and tails are joined to the beginning and end of a traffic block is proposed. A head (tail) gradually increases (decreases) the channel power by employing a pseudo-random bit sequence in which the probability of a “1” (“0”) increases from 0 to 0.5. This paper reports experimental results showing that EDFA optical power transients can be significantly reduced with adequate shaping periods. The effects of alternative shaping profiles are examined, and for a linear shaping profile, experiments show that the drop transient deviation is reduced by 0.5 dB while the add transient deviation is reduced by 0.71 dB. We show by lab experiments that the bit error rate induced by wavelength add-drop transients in a chain of EDFAs in an emulated fiber network can be reduced by 25% using power shaping techniques. Power shaping is an economical means of suppressing EDFA optical power transients compared to other physical layer approaches that require the addition of specialized components and can be applied to EDFAs as well as other solid-state and Raman optical amplifiers.

Decreasing EDFA transients by power shaping

Multi-wavelength optical networks make extensive use of erbium-doped optical amplifiers (EDFAs) to offset the effects of fiber attenuation and signal power splitting. As optical networking moves towards burst and packet switching, the effects of changes of optical power levels on one wavelength, or channel, can have an impact on the behavior of other wavelengths passing through the same amplifier and impair network performance. We have observed in our simulations of EDFA operation that both the amplitude and duration of EDFA transients will decrease when gradual changes are made to the input power of the EDFA. It was also verified in [D.H. Richards, J.L. Jackel, M.A. Ali, A theoretical investigation of dynamic all-optical automatic gain control in multichannel EDFA’s and EDFA cascades, J. Select. Top. Quantum Electron. 3 (4) (1997)] that the switching time of the channel dropping operation can influence the amplitude and duration of EDFA transients. We show that this effect can be exploited to successfully suppress EDFA transients by power shaping. Our approach is to increase/decrease the power of an added/dropped channel gradually, rather than abruptly. Power shaping can be implemented by adapting existing link layer protocols. It is general and can be applied to amplifiers using different technologies, including EDFAs, solid state and Raman amplifiers.

Passive and active optical bit-pattern recognition structures for multiwavelength optical packet switching networks

Next generation High-Speed optical packet switching networks require components capable of recognising the optical header to enable on-the-fly accurate switching of incoming data packets to their destinations. This paper experimentally demonstrates a comparison between two different optical header recognition structures; A passive structure based on the use of Fiber Bragg Gratings (FBGs), whereas the active structure employs Opto-VLSI processors that synthesise dynamic wavelength profile through digital phase holograms. The structures are experimentally demonstrated at 10Gbps. Performance comparison between the two structures is also discussed. These optical header recognition structures are attractive for multiwavelength optical network and applications.

Performance Evaluation of a Packet Switched Multi-wavelength Optical CDMA Network

In this paper an analytical model has been developed for a packet switched multi-wavelength optical CDMA network to study its system performance, while employing various two-dimensional optical codes. The model adopts Poisson distributed traffic implying infinite population assumption to reduce the computational complexity. It takes into account the packet errors due to chip interference between the code words. Further, guard time between chip pulses is introduced in order to relax the tunability requirements of the lasers in the wavelength hopped 2-D OCDMA scheme. Guard time reduces network speed and lowers the effective data transport. However the probability of receiving correct data packets is improved due to reduced chip interference. The combined impact of both on system behavior (throughput and delay) for different multi-wavelength codes is investigated.

End-to-End QoS Resource Management for an IP-Based DWDM Access Network

The ever-increasing use of broad-band Internet and complex multimedia applications is pushing fiber closer and closer to the homes. Within the European project IST HARMONICS (Hybrid Access Reconfigurable Multi-wavelength Optical Networks for IP-based Communication Services), an optical access feeder network and resource management framework were developed that tackle this demand for bandwidth and the desire to stimulate the convergence of last-mile access technologies. To cope with the lack of bandwidth in the access and last-mile networks and the different needs of applications and users, the developed management system provides end-to-end quality of service (QoS) while integrating multiple technologies. In this paper, a detailed overview of the end-to-end QoS management framework and novel time slot/wavelength MAC protocol for the optical feeder network is given. End-to-end QoS is based on Differentiated services (DiffServ) at layer 3, various QoS supporting technologies at layer 2, and QoS mappings between both layers. The paper will also focus on the field trial results of the HARMONICS project and give some guidelines for possible problems and solutions in this area.

A unified study of contention-resolution schemes in optical packet-switched networks

This paper presents a comprehensive study of contention-resolution schemes in a multiwavelength optical packet-switched network. This investigation aims to provide a unified study of a network of optical routers, which include contention resolution in wavelength, time, and space dimensions. Specifically, we show: 1) how to accommodate all three dimensions of contention resolution in an integrated optical router; 2) how the performance of the three dimensions compare with one another; and 3) how various combinational schemes can be designed and how they perform. With the representative architectures and network topologies studied in this paper, the simulation experiment results capture the characteristics of different contention-resolution schemes, and they quantify the upper-bound average offered transmitter load for these schemes. The combinational contention resolution schemes are shown to effectively resolve packet contention and achieve good network performance under light to intermediate load.

Advanced optical networking-Lucent's MONET network elements

The Multiwavelength Optical NETworking (MONET) Consortium is a five-year program that has been under way since December 1994. Its overall goal has been to research and prototype wavelength division multiplexing (WDM) optical networking technologies, network elements (NEs), and a network control and management system to support an advanced WDM optical networking testbed linking federal government agencies in the Washington, DC, area, including the National Security Agency (NSA), the Naval Research Laboratory (NRL), and the National Aeronautics and Space Administration (NASA). A major accomplishment for Lucent Technologies under the program has been the development of a new class of WDM NEs and associated supporting technologies in sufficient prototype quantities to populate the experimental agency network in Washington. This article describes the new network elements that were developed by the MONET Consortium for this new experimental optical network.

Accurate modeling of optical multiplexer/demultiplexer concatenation in transparent multiwavelength optical networks

This paper presents an accurate theoretical model for the study of concatenation of optical multiplexers/demultiplexers (MUXs/DMUXs) in transparent multiwavelength optical networks. The model is based on a semianalytical technique for the evaluation of the error probability of the network topology. The error-probability evaluation takes into account arbitrary pulse shapes, arbitrary optical MUX/DMUX, and electronic low-pass filter transfer functions, and non-Gaussian photocurrent statistics at the output of the direct-detection receiver. To illustrate the model, the cascadability of arrayed waveguide grating (AWG) routers in a transparent network element chain is studied. The performance of the actual network is compared to the performance of a reference network with ideal optical MUXs/DMUXs. The optical power penalty at an error probability of 10/sup -9/ is calculated as a function of the number of cascaded AWG routers, the bandwidth of AWG routers, and the laser carrier frequency offset from the channel's nominal frequency.