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Lightwave Technology, Journal of

Issue 13 • Date July1, 2008

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Displaying Results 1 - 25 of 39
  • [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): 1733 - 1734
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    Freely Available from IEEE
  • Interference Management in WLAN Mesh Networks Using Free-Space Optical Links

    Page(s): 1735 - 1743
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (739 KB) |  | HTML iconHTML  

    Frequency channels are assigned in wireless local-area network (WLAN) mesh networks subject to strict cochannel interference constraints. Since Wi-Fi may be freely used by other networks, added interference may eventually invalidate the original frequency assignment, making full link activation impossible. In this paper, we address this problem by selectively installing supplementary free-space optical (FSO) links when radio-frequency (RF) link performance has deteriorated. To minimize cost, the number of FSO links that are needed should be as small as possible. We first formulate the channel assignment problem with the objective of maximizing the number of simultaneous link activations while satisfying cumulative RF interference constraints. A proof is given for the NP-completeness of the joint frequency assignment and FSO link placement problem. We then propose an efficient heuristic to solve the channel assignment problem using a genetic algorithm. Results are then presented for various mesh networks which show that the proposed algorithm has good results compared with the computed bounds. The presented results show that the use of FSO links permits WLAN mesh network deployment in interference-prone situations. View full abstract»

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  • Fast Routing Algorithms for Lightpath Establishment in Wavelength-Routed Optical Networks

    Page(s): 1744 - 1751
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (490 KB) |  | HTML iconHTML  

    In this paper, we study shortest-path routing in wavelength-routed optical networks with an objective to optimize the average-case running time for path computation. Four fast routing algorithms are proposed for dynamically computing the shortest lightpaths or semilightpaths in a network with or without wavelength converters. To reduce the average-case running time for path computation, sequential search, backward routing, and informed search are used in the algorithm design. Simulation results show that the proposed algorithms can significantly reduce the average-case computational overhead for path computation as compared with existing algorithms. View full abstract»

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  • Layer 2 and 3 Contention Resolution and Radio-Over-Fiber in OCDMA PON for Transparent Optical Access in Personal Networks

    Page(s): 1752 - 1764
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1112 KB) |  | HTML iconHTML  

    In this paper, we analyze, for the first time, the eminent role of optical transparent networking in personal networks. We show how an optical access network mitigates many issues with respect to connectivity and mobility management. A concrete personal network user-scenario deduces requirements for such an architecture. A combination of passive optical network, optical code-division multiple access (OCDMA), and radio-over-fiber exhibits minimal cost and complexity because of centralized network control and management, resource sharing, and simplified network nodes. We enable transparent peer-to-peer communication between optical networking units in the OCDMA passive optical network subnet of the central office. We use, for the first time, simultaneously optical code-sense medium access control and optical code packet switching for contention resolution. View full abstract»

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  • Full-Duplex 1.0 Gbit/s Data Transmission Over 60 GHz Radio-on-Fiber Access System Based on the Loop-Back Optical Heterodyne Technique

    Page(s): 1765 - 1776
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    Full-duplex transmission over a 60 GHz radio-on-fiber access system based on the optical heterodyne technique is verified in this paper. With this technique, an optical carrier generator on the transmitting side consolidates the functions of wavelength and polarization control for optical heterodyne detection in uplinks and optical millimeter-wave generation in downlinks, on behalf of each optical transmitter/receiver. Therefore, the whole system configuration can be significantly simplified. A full-duplex 1.0 Gbit/s transmission experiment over 10 km of single-mode fiber, which represents an access network transmission, is demonstrated using the simultaneous modulation/photodetection operation of an electroabsorption modulator (EAM). Bit error rates of less than 10-9 were obtained in both the uplink and downlink without noticeable mutual interference, even though the laser source and the EAM is shared by both links, and no significant dispersion-induced degradation was observed. Moreover, the experimental results showed that an optical link budget of 9.2 dB can be achieved with the experimental configuration. View full abstract»

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  • The Data Vortex Optical Packet Switched Interconnection Network

    Page(s): 1777 - 1789
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    A complete review of the data vortex optical packet switched (OPS) interconnection network architecture is presented. The distributed multistage network topology is based on a banyan structure and incorporates a deflection routing scheme ideally suited for implementation with optical components. An implemented 12-port system prototype employs broadband semiconductor optical amplifier switching nodes and is capable of successfully routing multichannel wavelength-division multiplexing packets while maintaining practically error-free signal integrity (BER < 10-12) with median latencies of 110 ns. Packet contentions are resolved without the use of optical buffers via a distributed deflection routing control scheme. The entire payload path in the optical domain exhibits a capacity of nearly 1 Tb/s. Further experimental measurements investigate the OPS interconnection network's flexibility and robustness in terms of optical power dynamic range and network timing. Subsequent experimental investigations support the physical layer scalability of the implemented architecture and serve to substantiate the merits of the data vortex OPS network architectural paradigm. Finally, modified design considerations that aim to increase the network throughput and device-level performance are presented. View full abstract»

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  • A Framework for Evaluating the System Penalty From Polarization-Mode Dispersion Using Different Performance Monitoring Techniques

    Page(s): 1790 - 1797
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (686 KB) |  | HTML iconHTML  

    We present a theoretical framework relating system penalties from polarization-mode dispersion (PMD) to various monitoring techniques for non-return-to-zero systems. The framework includes models for string length, radio-frequency spectral power, eye opening, and degree of polarization. We validate the models experimentally and show that they are interrelated by common constants specific to the system under investigation. View full abstract»

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  • Secure OCDM Transmission Using a Planar Multiport Encoder/Decoder

    Page(s): 1798 - 1806
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (793 KB) |  | HTML iconHTML  

    We present different optical secure point-to-point transmission schemes using a planar multiport encoder/decoder. We consider both bit- and block-cipher cryptography: in the first case, each bit (both mark and space) from each user is encoded in a two-key optical code-division multiplexing signal. Block-cipher cryptography encodes a stream of n bits into a single code and corresponds to optical M-ary transmission. We demonstrate that block-ciphers are more secure with respect to bit-ciphers schemes and also against known-plaintext and chosen-plaintext attacks. View full abstract»

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  • Laser Optimization Guidelines for Dispersion Supported Transmission Systems Operating at Arbitrary Bit Rates

    Page(s): 1807 - 1816
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (576 KB) |  | HTML iconHTML  

    Laser guidelines for the performance optimization of dispersion supported transmission (DST) systems operating at arbitrary bit rates, not exceeding 40 Gbit-s-1, are presented. These laser guidelines are derived by numerical simulation for 40 Gbit-s-1 and analytically validated for other bit rates. The laser guidelines are settled in order to accomplish two DST system goals: maximizing the back-to-back sensitivity and the total dispersion tolerance, with fixed laser bias and modulation currents, thus avoiding the usual DST laser current tailoring to the fiber length. The laser optimization guidelines are expressed in terms of the intrinsic laser response parameters as in the following. The -3 dB intensity modulation (IM) bandwidth normalized by bit rate must be about 0.7; the zero of frequency modulation response normalized by bit rate must be about 0.75; the damping ratio of IM response must be about 0.7; the steady-state frequency deviation normalized by bit rate must be about 0.55; and the extinction ratio must be about 5.5. Numerical results show that these rules hold for lasers with parasitics with a cutoff frequency as low as 30% of bit rate, as well as for different current pulse shapes, laser gain, and compression models, and receiver electrical filters. View full abstract»

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  • Evaluation of Sensitivity of the Digital Coherent Receiver

    Page(s): 1817 - 1822
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (329 KB) |  | HTML iconHTML  

    In this paper, we investigate the sensitivity of the digital coherent receiver both theoretically and experimentally. The receiver sensitivity close to the shot-noise limit is demonstrated in the 10-Gbit/s binary phase-shift keying system with the help of a low-noise optical preamplifier. We also introduce polarization diversity into our receiver. Maximal-ratio polarization combining in the digital domain makes the receiver sensitivity independent of the state of polarization of the incoming signal without power penalty. View full abstract»

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  • Automatic PMD Compensation by Unsupervised Polarization Diversity Combining Coherent Receivers

    Page(s): 1823 - 1834
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1189 KB) |  | HTML iconHTML  

    A new automatic scheme to compensate the intersymbol interference caused by fiber polarization mode dispersion (PMD) is introduced. The proposed method makes use of the orthogonal polarization components by combining them through adaptive electronic filters, which are adjusted through a low-complexity unsupervised updating method. The simplicity of the proposed unsupervised method is its most critical feature in terms of enabling real-time and all-hardware implementation. Simulation results are provided for a fiber channel with 40 Gsymbols/s signalling rate and a mean DGD level greater than the symbol period, where it is demonstrated that the PMD can be effectively compensated with a 2 dB signal-to-noise ratio penalty relative to PMD-free channel. View full abstract»

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  • Characterization of the Dynamic Absorption of Electroabsorption Modulators With Application to OTDM Demultiplexing

    Page(s): 1835 - 1839
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (161 KB) |  | HTML iconHTML  

    In this paper, a technique for characterizing the dynamic absorption of electroabsorption modulators (EAMs) under high-frequency sinusoidal modulation is described. By using an optical sampling oscilloscope (OSO), the nonlinear response of a modulator to 10- and 40-GHz modulation is accurately measured. The results for the dynamic absorption are used in a measurement-based model to calculate optical gating windows for the demultiplexing of a 160-Gb/s optical time-division multiplexed (OTDM) signal to its 10- and 40-Gb/s tributary signals. Good agreement is achieved between the calculated and measured gating windows. View full abstract»

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  • Design Rules for Single-Mode and Polarization-Independent Silicon-on-Insulator Rib Waveguides Using Stress Engineering

    Page(s): 1840 - 1846
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (693 KB) |  | HTML iconHTML  

    There is a trend towards miniaturization of silicon photonic circuits due to superior performance and small cost. Design rules that must be imposed on the geometry of optical waveguides to make them behave as polarization-independent and single-mode devices are well known for waveguides with relatively large cross sections and for some small cross-sectional rib waveguides with vertical sidewalls and an air top cladding. The influence of the top oxide cover on waveguide birefringence was analyzed recently, but only for relatively large cross-sectional waveguides. This paper reports simulations for both single-mode and polarization-independent behavior for small cross-sectional waveguides with variable rib width, etch depth, top oxide cover thickness, and side-wall angle. The results show that the stress-induced effects must be taken into account to satisfy both requirements. Design rules to maintain birefringence-free operation and to satisfy single-mode behavior for small rib silicon-on-insulator (SOI) waveguides are presented. View full abstract»

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  • Nonlinear Interaction Between Signal and Noise in Optical Fibers

    Page(s): 1847 - 1853
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    A model suitable for analyzing the nonlinear interaction between signal and noise, mediated by the Kerr effect in optical communication systems, is presented. This model treats separately signal and noise and permits analysis of the symbols' central time position and frequency evolution. It is shown that this nonlinear interaction between signal and noise leads to symbols' random frequency shifts, which induce timing jitter in all types of systems. We also discuss the problem of estimating timing jitter for a signal embedded in noise. View full abstract»

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  • Investigation of Strain- and Temperature-Dependences of Brillouin Frequency Shifts in GeO _{2} -Doped Optical Fibers

    Page(s): 1854 - 1861
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    The dependences of Brillouin frequency shifts (BFSs) on strain and temperature in GeO2-doped optical fibers are investigated. Our study shows that the strain (temperature) coefficient of the BFS is linearly proportional to the decrease of the GeO2 concentration in the fiber core with a relative rate of -1.48% (-1.61%) per unit mol percentage. The coefficients of 0 mol% GeO2 -doped silica (i.e., pure silica) are extracted from the least squares fitted linear dependences of the coefficients on GeO2 concentration; the results show good agreement with simulations taking into account the changes of the refractive index, the density, and the Young's modulus induced by the applied strain and the temperature change. Furthermore, when measurement upon three fibers drawn from the same preform, but under different draw tensions are done, this provides that there exists an optimized tension during fiber fabrication that maximizes the difference between strain and temperature coefficients. View full abstract»

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  • Polarization-Maintaining Large-Mode-Area Microstructured-Core Optical Fibers

    Page(s): 1862 - 1867
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    A novel polarization-maintaining large-mode-area optical fiber is proposed in this paper. Anisotropic microstructured core in the fiber is realized by the inclusion of air holes arranged in rectangular lattice. An updoped silica background is introduced to compensate the reduction of the effective core index induced by the air holes. Numerical investigation demonstrated high birefringence on the order of 10-3 and hexagonal profile mode fields with mode areas as large as of 161.2 and 118.0 mum2, at the wavelength of 1.55 mum, for x- and y-polarized states, respectively, can be achieved in one such fiber. In contrast to polarization-maintaining optical fibers reported previously, the birefringence of the fiber is increasing with the increase of frequency. We also proposed a novel kind of single-polarization single-mode optical fibers based on the design, and one such fiber presents mode area as large as 119 mum2 and operating wavelength as broad as 127 nm with confinement loss below 0.1 dB/km. View full abstract»

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  • Improved Full-Vector Finite-Difference Complex Mode Solver for Optical Waveguides of Circular Symmetry

    Page(s): 1868 - 1876
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    An improved full-vector finite-difference (FD) complex mode solver for circularly symmetric optical waveguides is developed and validated. The formulations are derived from Taylor expansion of transverse electric and magnetic fields and match of boundary conditions at radial index discontinuities. Calculation of the guided and leaky modes of step index fibers, Bragg fibers, and surface plasmon polaritons structures shows significant improvement in terms of accuracy and rate of convergence without increase of computational efforts, in comparison with the conventional FD scheme based on the average-index approximation. It is demonstrated that the performance of the new scheme is robust for high-order modes and waveguides with high index contrast. Contrary to the conventional FD solvers that claim the magnetic field formulation is more rigorous than the electric field formulation, the improved solver yields practically identical results for both formulations. View full abstract»

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  • Guiding Properties of Silica/Air Hollow-Core Bragg Fibers

    Page(s): 1877 - 1884
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    The guiding properties of realistic silica/air hollow-core Bragg fibers have been investigated by calculating the dispersion curves, the confinement loss spectrum, and the field distribution of the guided modes through a full-vector modal solver based on the finite-element method. In particular, the silica bridge influence on the fundamental mode has been analyzed by comparing the properties of an ideal structure, without the silica nanosupports, and of two realistic fibers, with squared off and rounded air-holes. Simulation results have demonstrated the presence of anticrossing points in the dispersion curves, associated to the transition of the fundamental mode into a surface mode. It has been shown that surface modes are responsible for the sharp loss peaks, also experimentally measured, which pollute the loss spectrum of the fundamental mode and of the higher order modes. Then, the influence on the guiding properties of each geometric characteristic in the hollow-core Bragg fiber cross-section has been deeply investigated, thus showing which parameter it is better to change in order to properly modify the loss values or its spectral behavior. Moreover, in order to improve the loss properties of hollow-core Bragg fibers, the number of silica and air layers in the fiber cladding has been increased, and the layer thickness has been modified. Results have shown that the first change is more effective for the loss reduction, while the second is useful for a spectral shift. Finally, among the different possible applications, the feasibility of a DNA biosensor based on a hollow-core Bragg fiber has been demonstrated. View full abstract»

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  • Tunable Ultranarrow Dual-Channel Filter Based on Sampled FBGs

    Page(s): 1885 - 1890
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    A new kind of ultranarrow dual-bandpass fiber Bragg grating is proposed and demonstrated, for the first time to the author's best knowledge, with a symmetrical technique in which the first and second half gratings are sampled with the period of 0-and-pi and pi-and-0, respectively. This kind of grating can achieve dual-wavelength operation with a symmetrical spectrum. The unique spectral property of the proposed gratings is analyzed by means of Fourier theory and confirmed experimentally. By integrating the proposed grating with the 0-and-pi sampling grating, an ultranarrow dual-channel filter is designed in principle and demonstrated experimentally whose 3-dB bandwidth is less than 1 pm. By stretching the gratings, the two wavelengths of the proposed filter can be tuned whereas their channel spacing remains unchanged. View full abstract»

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  • Fabrication and Characterization of Temperature Insensitive 660-nm Resonant-Cavity LEDs

    Page(s): 1891 - 1900
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    InGaP/AlGaInP 660-nm resonant-cavity light-emitting diodes (RCLEDs) with stable temperature characteristics have been achieved by extending the resonant cavity length from one optical wavelength (1 lambda) to three optical wavelengths (3 lambda) and tripling the number of quantum wells. When the operation temperature increases from 25degC to 95degC, the degree of power variation at 20 mA is reduced from -2.1 dB to -0.6 dB for the conventional 1- lambda cavity RCLEDs and 3- lambda cavity RCLEDs, respectively. In order to interpret the temperature-dependent experimental results, advanced device simulation is applied to model the RCLEDs with different cavity designs. According to the numerical simulation results, we deduce that the stable temperature-dependent output performance should originate from the reduction of electron leakage current and thermally enhanced hole transport for the 3- lambda cavity AlGaInP RCLEDs. View full abstract»

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  • Frequency and Duration of Communication System Outages Resulting From Polarization Mode Dispersion

    Page(s): 1901 - 1908
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    In this paper, we employ measurements of transponder tolerance to both differential group delay (DGD) and second-order polarization mode dispersion (SOPMD) and of the temporal evolution of DGD and SOPMD in installed transmission systems to predict the influence of PMD on the rate and duration of PMD-induced system outages. An empirical 2-D random-walk model predicts that the outage rate and duration depends solely on the mean fiber DGD. We find that the step size of the random walk is nearly uncorrelated with the instantaneous value of the PMD. We then justify the assumptions of this procedure with a full numerical simulation and employ a biased Markov chain algorithm to generate highly accurate results for system outages where simplified models fail. View full abstract»

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  • Tailoring Dispersion and Confinement Losses of Photonic Crystal Fibers Using Hybrid Cladding

    Page(s): 1909 - 1914
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    We present a hybrid cladding photonic crystal fiber (PCF) for shaping nearly zero ultraflattened dispersion and low confinement losses in a wide range of wavelengths. The finite difference method with anisotropic perfectly matched boundary layer is used to investigate the guiding properties. It has been shown theoretically that it is possible to obtain nearly zero ultraflattened dispersion of 0 plusmn0.25 mups/nm/km in a wavelength range of 1.44 to 2.0 mum with low confinement losses less than 0.005 dB/km within the entire band of interest from a five-ring hybrid cladding PCF. View full abstract»

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  • Fused Fiber Couplers Made Wavelength Insensitive by the Glass Structure Change

    Page(s): 1915 - 1920
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    In this paper, a method based on the glass structure change is proposed to make fused fiber couplers wavelength insensitive. After fused fiber couplers are fabricated, the coupling regions are heated unequally by arc discharge. The glass structure change induced by arc discharge generates unbalance index changes in the two identical fibers constituting the fused fiber couplers, and brings about the phase mismatch between the fibers. The phase mismatch results in the wavelength-insensitive response. The proposed method was applied to wavelength-flattening fused fiber couplers with different cross-sectional shapes, and it has become clear that the method is effective for the reduction of the wavelength dependence. 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