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Lightwave Technology, Journal of

Issue 8 • Date Aug. 2007

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Displaying Results 1 - 25 of 52
  • [Front cover]

    Page(s): C1
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    Freely Available from IEEE
  • Journal of Lightwave Technology publication information

    Page(s): C2
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    Freely Available from IEEE
  • Table of contents

    Page(s): 1881 - 1882
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    Freely Available from IEEE
  • Optimal Burst Scheduling in Optical Burst Switched Networks

    Page(s): 1883 - 1894
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (777 KB) |  | HTML iconHTML  

    Optical burst switching (OBS) is an emerging technology that allows variable size data bursts to be transported directly over dense wavelength division multiplexing links. In order to make OBS a viable solution, the burst-scheduling algorithms need to be able to utilize the available wavelengths efficiently, while being able to operate fast enough to keep up with the burst incoming rate. For example, for a 16-port OBS router with 64 wavelengths per link, each operating at 10 Gb/s, we need to process one burst request every 78 ns in order to support an average burst length of 100 kB. When implemented in hardware, the well-known horizon scheduler has O(1) runtime for a practical number of wavelengths. Unfortunately, horizon scheduling cannot utilize the voids created by previously scheduled bursts, resulting in low bandwidth utilization. To date, minimum starting void is the fastest scheduling algorithm that can schedule wavelengths efficiently. However, while its complexity is O(log m), it requires 10 log m memory accesses to schedule a single burst. This means that it can take up to several microseconds for each burst request, which is still too slow to make it a practical solution for OBS deployment. In this paper, we propose an optimal burst scheduler using constant time burst resequencing (CTBR), which has O(1) runtime. The proposed CTBR scheduler is able to produce optimal burst schedules while having processing speed comparable to the horizon scheduler. The algorithm is well suited to high- performance hardware implementation. View full abstract»

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  • A New Method for Solving Routing and Wavelength Assignment Problems in Optical Networks

    Page(s): 1895 - 1909
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (533 KB) |  | HTML iconHTML  

    The standard Lagrangian relaxation (SLR) method is an efficient method for solving the routing and wavelength assignment (RWA) problems in optical networks. However, previous work did not deal with multiple connection requests with identical source and destination pairs, which are frequently encountered in practice and can cause serious issues when using SLR. More specifically, in solving the dual subproblems after the wavelength capacity constraints are relaxed, the shortest path algorithms such as Dijkstra's typically assign the same route to such connection requests, which possibly leads to a poor RWA solution. In this paper, we introduce a new method, i.e., the successive subproblem solving (SSS) method and one of its implementations, within the Lagrangian relaxation framework. The essence of SSS is to introduce coupled penalty terms and use the surrogate subgradients for search direction at the high level. The homogenous subproblems at the low level are then solved sequentially to avoid the nondecomposable difficulty. Theoretical analysis is performed to provide convergence proof. Numerical results are presented to show that the new method is effective and efficient. View full abstract»

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  • Synchronous Walsh-Based Bipolar–Bipolar Code for CDMA Passive Optical Networks

    Page(s): 1910 - 1917
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (405 KB) |  | HTML iconHTML  

    We propose a "synchronous" wavelength-time optical code-division multiple access (CDMA) scheme using 2D Walsh-based bipolar-bipolar code, in which Walsh code sequences are used for time spreading, in place of Barker sequences used in our previously proposed ldquoasynchronousrdquo bipolar-bipolar code. The new synchronous coding scheme supports larger cardinality and better performance than the asynchronous scheme because Walsh code has a larger cardinality than Barker sequences and has a zero cross-correlational property at the expense of system synchronization. One potential application is future CDMA-based passive optical networks, in which synchronous downstream traffic uses the Walsh-based bipolar-bipolar code and asynchronous upstream traffic uses the Barker-based counterpart. Since the new code is modified from the original code, the same hardware can be used for both directions of traffic. View full abstract»

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  • Migration Strategies Toward All Optical Metropolitan Access Rings

    Page(s): 1918 - 1930
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (921 KB) |  | HTML iconHTML  

    Nowadays, network operators are steadily deploying optical circuit switching (OCS) equipment in their metropolitan networks in order to cope with traffic increase and, most importantly, in order to reduce capital expenditures and operational expenditures of existing active technologies. On the other hand, optical burst switching (OBS) technology is expected to become mature in the medium term, and it may be used as an alternative to current OCS networks due to its potential advantages in terms of bandwidth allocation granularity. While OBS is being extensively studied in the literature, little attention has been paid in conducting a comparative analysis of OBS versus OCS, especially concerning cost analysis. In this paper, we provide a comparative analysis of OBS versus OCS as an evolutionary technology for all-optical rings in the metropolitan-access network. This paper is specifically targeted toward optimizing the number of optoelectronic receivers and wavelengths with real traffic matrices from the metropolitan rings in Madrid, Spain. Such matrices also include traffic projections of foreseeable broadband services, which are based on a market analysis from the largest operator in Spain. Our findings show that OCS might be more efficient than OBS in the metro-access segment, which is characterized by a highly centralized traffic pattern. However, the more distributed the traffic is, the more efficient the OBS is as well. Consequently, OBS might be better suited to metro-core networks, which show a more distributed and dynamic traffic pattern. View full abstract»

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  • Robust Design for Reconfigurable Coder/Decoders to Protect Against Eavesdropping in Spectral Amplitude Coding Optical CDMA Networks

    Page(s): 1931 - 1948
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1692 KB) |  | HTML iconHTML  

    This paper presents an enhanced security mechanism to protect spectral-amplitude-coding optical code-division multiple-access networks against eavesdropping. This study proposes an alternative to huge code-space size techniques such as wavelength hopping/time spreading or spectral-phase coding for network protection against eavesdropping by exploiting the cyclic properties of arrayed-waveguide-grating routers and maximal-length sequence code (M-sequence code). In addition, the network is protected using a dynamic reconfigurable coding/decoding scheme based on optical switches and a dynamic code matrix assignment scheme implemented using simple electrical shift registers. The signal-to-beat noise ratio is evaluated for various data bit rates to provide an indication of the confidentiality of the power level for a specified bit error rate (Pe<10-9). To further verify the effectiveness of the proposed scheme, this paper investigates a weighted load balance problem based on the power distribution of each transmitted wavelength under various eavesdropping abilities. A dynamic codeword modification is proposed which identifies the code matrix assignment that minimizes the degree of weighted load balance (DWLB). The evaluation results show that the reconfiguration policy outperforms one class of static policies in terms of two performance metrics, namely, the DWLB and the number of register shifts required to reconfigure the code matrix assignment. View full abstract»

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  • Contour-Based Priority Scheduling in Optical Burst Switched Networks

    Page(s): 1949 - 1960
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1448 KB) |  | HTML iconHTML  

    Optical burst switching (OBS) is an emerging technology that allows variable size data bursts to be transported directly over dense wavelength division multiplexing links. Although several quality-of-service (QoS) schemes have been proposed for OBS networks, how to provide QoS at the high speed required by the OBS network is still an open question. In this paper, we propose a novel O(1) runtime contour-based priority algorithm that provides complete priority isolation among different priorities. This is the first practical O(1) runtime priority algorithm proposed for OBS, and it is well suited to high-speed hardware implementation. View full abstract»

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  • Design and Fabrication of Low-Driving-Voltage Electroabsorption Modulators Operating at 40 Gb/s

    Page(s): 1961 - 1969
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (917 KB) |  | HTML iconHTML  

    In this paper, a design for low-driving-voltage InGaAlAs/InAlAs electroabsorption modulators (EAMs) operating at 40 Gb/s is described. The theoretical calculation clarified that the tensile-strained InGaAlAs/InAlAs multiquantum-well layers with thin wells provide large and steep extinction characteristics. This was experimentally confirmed. We modeled an EAM with a low-loss coplanar waveguide for both the input and output ports and designed an optimized core structure that assures a sufficient extinction ratio and electrical-to-optical bandwidth for 40-Gb/s operation, in terms of well number and core length. A fabricated device driven by a peak-to-peak voltage as low as 1.1 V shows a 3-dB bandwidth of over 50 GHz and an RF extinction ratio of 10 dB. Error-free operation at 40 Gb/s is confirmed. View full abstract»

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  • A Wavelength-Division-Multiplexed Passive Optical Network With Flexible Optical Network Unit Internetworking Capability

    Page(s): 1970 - 1977
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (421 KB) |  | HTML iconHTML  

    We propose and experimentally demonstrate a novel flexible optical network unit (ONU) internetworking architecture over a wavelength-division multiplexed passive optical network (WDM-PON). By employing our designated wavelength assignment and remodulating the downstream differential phase-shift keying signal as the ONU internetworking carrier, one ONU can broadcast its own message to all other ONUs, with negligible signal interference. Moreover, the inter-ONU communication can further be partitioned into arbitrary virtual private groups of ONUs by employing designated RF tones for identification and control. It was experimentally demonstrated that the performance degradation due to the introduction of RF tones is negligible compared with the full broadcast case. Our proposed scheme can provide high flexibility and practical implementation for WDM-PONs. View full abstract»

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  • A Quantized Delay Buffer Model for Single-Wavelength Fiber Delay Line Buffer

    Page(s): 1978 - 1985
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (524 KB) |  | HTML iconHTML  

    The fiber delay line (FDL) buffer is widely used in optical packet switching networks for contention solution. In this paper, a quantized delay buffer model is proposed to analyze the performance of the single-wavelength FDL buffer. Considering the delay quantization in the FDLs, the delay time and the waiting time of the packet are discussed. Without specific assumptions of the packet arrival process and length distribution, the model presents a generic approach to study the delay time distribution and modify the integral equation for the waiting time distribution. Analytic and exact results of the two aforementioned distributions can be obtained without any approximation. The accuracy of the model is validated through simulation. View full abstract»

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  • Dispersion-Compensation Schemes for 160-Gb/s 1200-km Transmission by Optical Phase Conjugation

    Page(s): 1986 - 1995
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (352 KB) |  | HTML iconHTML  

    Appropriate dispersion management possesses the superiority to relax the limitation of nonlinearities in high-speed transmission systems employing optical phase conjugation (OPC). In this paper, several dispersion-compensation schemes have been analytically and numerically investigated in a 160-Gb/s OPC system. A comprehensive performance comparison of these schemes over 1200-km transmissions has been carried out to present a reference for future OPC system designs. The scheme with a gradient dispersion map is recommended, particularly for G.655 fiber with a relatively low local dispersion. View full abstract»

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  • Localized High Birefringence Induced in SMF-28 Fiber by Femtosecond IR Laser Exposure of the Cladding

    Page(s): 1996 - 2001
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (327 KB) |  | HTML iconHTML  

    A process for creating a local high fiber birefringence and large variation in refractive-index modulation with a polarization in fiber Bragg gratings using post writing exposures with femtosecond pulses is presented. A birefringence as high as ~8 times 10-4 was obtained in the core of SMF-28 fiber by exposing the cladding of the fiber in close proximity to the core/cladding interface with a modulated multibeam interference field created by a phase mask. The birefringence is likely due to the induced stress rather than the direct asymmetric refractive index modification. View full abstract»

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  • Nonlinear Phase Noise in Optical-Fiber-Communication Systems

    Page(s): 2002 - 2032
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3713 KB) |  | HTML iconHTML  

    Gordon and Mollenauer, in their famous paper published in 1990, laid out how the interplay between the nonlinear Kerr effect in optical fibers and the amplified spontaneous-emission (ASE) noise from the optical-amplifiers results in enhanced levels of noise and degrades the performance of modulation schemes that encode information in, particularly, the phase of the optical carrier. This phenomenon has been termed as nonlinear phase noise in the literature. In this paper, we first present a comparative and critical review of previous techniques that have been proposed for the analysis of nonlinear phase noise by forming a classification framework that reveals some key underlying features. We then present a unifying theory and a comprehensive methodology and computational techniques for the analysis and characterization of nonlinear phase noise and its impact on system performance by building on and extending previous work that we identify as most favorable and systematic. In our treatment, we consider a multichannel multispan optically amplified dense wavelength-division multiplexed system and develop general techniques for the analysis of the intricate interplay among Kerr nonlinearity, chromatic dispersion, and ASE noise, and for computing the bit-error-ratio performance of differential phase-shift-keying (DPSK) systems. By means of the extensive results we present, we demonstrate and argue that correlated noise behavior plays a most significant role in understanding nonlinear phase noise and its impact on DPSK system performance. View full abstract»

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  • Digital Equalization of Chromatic Dispersion and Polarization Mode Dispersion

    Page(s): 2033 - 2043
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (342 KB) |  | HTML iconHTML  

    In this paper, we consider a fractionally spaced equalizer (FSE) for electronic compensation of chromatic dispersion (CD) and polarization-mode dispersion (PMD) in a dually polarized (polarization-multiplexed) coherent optical communications system. Our results show that the FSE can compensate any arbitrary amount of CD and first-order PMD distortion, provided that the oversampling rate is at least 3/2 and that a sufficient number of equalizer taps are used. In contrast, the amount of CD and PMD that can be corrected by a symbol-rate equalizer only approaches an asymptotic limit, and increasing the number of taps has no effect on performance due to aliasing that causes signal cancellation and noise enhancement. View full abstract»

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  • Optimal Resource Allocation Scheme in a Multirate Overlapped Optical CDMA System

    Page(s): 2044 - 2053
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (758 KB) |  | HTML iconHTML  

    This paper addresses the problem of resource allocation in a multiservice optical network based on an overlapped code-division-multiple-access system. A joint transmission power and overlapping coefficient (transmission rate) allocation strategy is provided via the solution of a constrained convex quadratic optimization problem. The solution of this problem maximizes the aggregate throughput subject to peak laser transmission power constraints. The optimization problem is solved in a closed form, and the resource allocation strategy is simple to implement in an optical network. Simulation results are presented, showing a total agreement between the derived analytical solution and the one obtained using a numerical search method. In addition, analytical and numerical results show that the proposed resource allocation strategy can offer substantial improvement in the system throughput. View full abstract»

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  • Analysis of PMD-Induced System Penalty Using Pulse Spreading

    Page(s): 2054 - 2059
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (830 KB) |  | HTML iconHTML  

    This paper presents a technique that predicts the polarization-mode-dispersion (PMD)-induced system penalty based on rms pulse spreading. Amplifled-spontaneous-emission noise limited and thermal noise limited cases are investigated for the nonreturn to zero (NRZ) and return to zero modulation formats. A comparison is made with similar approaches that use three alternative metrics: the string length up to first order, the conventional string length, and the weighted string length. It is shown that the technique based on pulse spreading extends the applicable range of the system-penalty prediction in terms of both the mean link PMD and the modulated-signal bandwidth. View full abstract»

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  • Intersymbol Interference (ISI) Suppression Technique for Optical Binary and Multilevel Signal Generation

    Page(s): 2060 - 2068
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (648 KB) |  | HTML iconHTML  

    An intersymbol interference (ISI)-suppressed optical multilevel modulation technique that is applicable to a wide range of binary and multilevel signaling is proposed. It employs binary phase-shift keying modulations that are generated by Mach-Zehnder intensity modulators as basic building blocks, and complex multilevel modulations are synthesized using interferometric addition and tandem modulations. Its feasibility and ISI suppression effect are verified in various binary and multilevel signal synthesis schemes using numerical simulations. Furthermore, the generation of ISI-suppressed zero-chirp binary and quaternary amplitude-shift keying modulations is experimentally demonstrated. Finally, its applicability to complex optical multilevel signaling is shown in the generation of a 40-Gb/s 16-level amplitude- and phase-shift keying signal, which results in 3-dB sensitivity improvement compared with the one using a conventional four-level electrical driving signal. View full abstract»

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  • Performance of Nonlinear Receivers in Asynchronous Spectral-Phase-Encoding Optical CDMA Systems

    Page(s): 2069 - 2080
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1264 KB) |  | HTML iconHTML  

    Because of limits on the speed of the photodetector, a nonlinear thresholder is needed at the receiver of a spectral-phase-encoding optical code-division multiple-access system to discriminate between the correctly decoded short pulse and the low-intensity interference. The two most common nonlinear receivers based on second harmonic generation and self-phase modulation effects are analyzed in this paper. Mathematical models are provided, and analytical results are obtained to estimate the receivers' performances. Numerical simulations are carried out for both receivers with different system parameters. Both m-sequences and random binary codes are examined for spreading. The results provide a profile of how these nonlinear receivers perform with various system settings. It is found that, when an m-sequence is used as the spreading code, the encoded signal does not obey Gaussian statistics, and the system performs better than an equivalent system using a random code. View full abstract»

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  • WDM-Compatible Channel Scrambling for Secure High-Data-Rate Optical Transmissions

    Page(s): 2081 - 2089
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1350 KB) |  | HTML iconHTML  

    We propose a noninvasive optical encryption technique, taking advantage of the specificities of the physical layer of a backbone transmission network, to secure optical transmissions at high data rates ( >10 Gb/s). Our goal is to secure data transmission without impacting the physical layer by guaranteeing the transparency of the encryption technique with respect to the transmission equipment. The proposed method belongs to the optical code-division multiple-access technique using spectral-phase encoding, based on pulse-overlapping sequence. The goal is to scale the protection levels to different threat and attack scenarios and to make them resilient to intrusions and robust to fiber-propagation parameters. In this paper, linear and nonlinear transmission effects (where self- and cross-phase modulations become important) are considered to maintain the quality of transmission. Finally, particular attention is paid to the ciphering key transmission for which we propose an adapted solution. View full abstract»

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  • On the Decision-Feedback Equalizer in Optically Amplified Direct-Detection Systems

    Page(s): 2090 - 2097
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (233 KB) |  | HTML iconHTML  

    This paper investigates the combined feed-forward and decision-feedback equalizer (DFE) in a lightwave system with optical amplifiers and a direct-detection receiver. Based on a nonlinear channel model, the paper provides a modification of the classical minimum mean square error theory of the DFE. Furthermore, an analytical method that is capable of accurate bit error rate (BER) evaluation is used to optimize the DFE for minimum BER. The paper evaluates the DFE performance for both optical ON-OFF keying and duobinary modulation formats in the presence of chromatic dispersion as well as the DFE performance for the mitigation of higher order polarization mode dispersion in first-order compensated systems. The paper shows that the DFE can compensate for the BER degradation due to narrow-band receiver-side optical filtering and can significantly improve the spectral efficiency of dense wavelength-division multiplexed systems. View full abstract»

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  • Optimized All-Fiber Supercontinuum Source at 1.3 μm Generated in a Stepwise Dispersion-Decreasing-Fiber Arrangement

    Page(s): 2098 - 2102
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (148 KB) |  | HTML iconHTML  

    In this paper, the generation of a continuous-wave (CW)-pumped supercontinuum (SC) source at 1.3 mum is described. The device makes use of a tunable Yb-doped fiber laser, a cascade of fiber Bragg grating mirrors, and a concatenation of standard silica fibers with stepwise decreasing dispersion. It is shown that the dispersion-decreasing-fiber set enhances the width of the generated SC, since it favors the fission of the CW input into high-order solitons. The generated SC spans from 1280 to 1513 nm, shows an average output power of 1.34 W, and exhibits >0-dBm/nm spectral density of over 200 nm. View full abstract»

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  • Investigation of a Downsized Silica Highly Nonlinear Fiber

    Page(s): 2103 - 2107
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (295 KB) |  | HTML iconHTML  

    Theoretical influences of reducing the cladding diameter for silica highly nonlinear fiber (HNLF) have been investigated by the finite-element method. Downsized HNLF with 56-mum cladding was fabricated, and certain reliability was confirmed through mechanical and environmental tests. A coin-sized module was obtained using over 200 m of 56-mum HNLF. View full abstract»

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  • Highly Efficient S-Band Thulium-Doped Fiber Amplifier Employing High-Thulium-Concentration Doping Technique

    Page(s): 2108 - 2114
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (328 KB) |  | HTML iconHTML  

    In the paper, we describe in detail a highly efficient S-band thulium-doped fiber amplifier (TDFA) employing a high-thulium-concentration doping technique. A TDFA with a dual-pass configuration is superior to a TDFA with a single-pass configuration with regard to power-conversion efficiency, whereas it is inferior with regard to noise figure (NF). We propose a cascaded configuration consisting of a single- and double-pass configuration, which provides high efficiency and a low NF. The configuration generated no interference noise, which can result from multipass interference (MPI) with a double-pass configuration. We achieved gains exceeding 26 dB and NFs of less than 7 dB in the 1480-1510-nm wavelength region (30-nm bandwidth). Furthermore, an 8 times 10-Gb/s transmission experiment also confirmed that there was no MPI-induced excess noise. View full abstract»

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Aims & Scope

The Journal of Lightwave Technology contains articles on current research, applications and methods used in lightwave technology and fiber optics.

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
Peter J. Winzer
Alcatel-Lucent Bell Labs