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Lightwave Technology, Journal of

Issue 5 • Date March1, 2008

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

    Page(s): C1
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  • Journal of Lightwave Technology publication information

    Page(s): C2
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  • Table of contents

    Page(s): 465 - 466
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  • Distortion of OFDM Signals on Radio-Over-Fiber Links Integrated With an RF Amplifier and Active/Passive Electroabsorption Modulators

    Page(s): 467 - 477
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1908 KB) |  | HTML iconHTML  

    The integration of orthogonal frequency division multiplexing (OFDM) and radio-over-fiber (RoF) techniques have made cost-effective and high-data-rate mobile wireless Internet networks possible, such as wireless broadband networks. This paper describes the distortion effects of OFDM signals fed via an RF amplifier integrated with an RoF link employing active and passive electroabsorption modulators (EAM) for chiefly broadband in-building network applications. First, peak-to-average power ratio was investigated for RoF links. Second, the adjacent channel power ratio, which estimates the degree of spectral re- growth due to the in-band and out-of-band interference resulting from distortion effects from nonlinear amplification, error vector magnitude, and system distortion effects, was also observed for the proposed system. In this study, we considered a combined Volterra-series and impulse response-based analytical model for WiBro systems and compared it to the observed measurements. We analyzed the different nonlinear distortion effects for OFDM signals driven via an RF amplifier that was integrated with an RoF link employing a distributed feedback laser as a transmitter and an active and passive InP EAM as a receiver. The results show significant agreement between the suggested analytical model and the measurement case. This study is unique in that it examines the distortion effects of RoF links with active and passive EAMs as an access point for OFDM-based wireless access networks. View full abstract»

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  • LDPC-Coded MIMO Optical Communication Over the Atmospheric Turbulence Channel

    Page(s): 478 - 487
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    In this paper, coded multiple-input-multiple-output (MIMO) communication schemes for data transmission over the optical atmospheric turbulence channels are studied. Two strategies are proposed and compared. The first is based on repetition coding, and the second on space-time (ST) coding. Both approaches employ low-density parity-check (LDPC) codes. The LDPC codes are designed using the concept of pairwise balanced design (PBD), balanced incomplete block design (BIBBD), and block-circulant (array) codes. To improve the spectral efficiency, we employ a bit-interleaved (BI) LDPC-coded modulation based on the pulse amplitude modulation (PAM). A better bit error rate (BER) performance is achieved by the iteration of extrinsic information between a demapper and LDPC decoder. The simulations show that the LDPC-coded MIMO schemes can operate under a strong atmospheric turbulence and at the same time provide excellent coding gains compared with the transmission of uncoded data. To verify the efficiency of the proposed coding schemes, achievable information rates are computed when the turbulence is modeled by a gamma-gamma distribution. View full abstract»

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  • Directional Coupler Formed by Photonic Crystal InAlGaAs Nanorods

    Page(s): 488 - 491
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    In this paper, we demonstrate the use of photonic crystal (PC) directional couplers to separate light of wavelengths at 1.31 and 1.55 m. The PC structure consists of InAlGaAs nanorods arranged in hexagonal lattice. The simulation of our device is implemented by the finite-difference time-domain method. The devices are fabricated by e-beam lithography and conventional photolithography. We use the strong inverse method (SIM) of e-beam lithography to make the pattern smoother. The measurement results confirm that 1.31/1.55-m wavelength splitter can be realized in PC structures formed by nanorods. View full abstract»

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  • Stimulated Brillouin Scattering in a Single-Mode Tellurite Fiber for Amplification, Lasing, and Slow Light Generation

    Page(s): 492 - 498
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (902 KB) |  | HTML iconHTML  

    In this paper, Brillouin gain performances of tellurite fiber are investigated for photonics applications. We demonstrate stimulated Brillouin amplification and lasing and the simulated performance of slow light generation in a single-mode tellurite fiber. A Brillouin gain of 29 dB is achieved in a 100-m tellurite fiber with a pump power of 10 mW at 1550 nm. A peak value of Brillouin gain coefficients of 1.6989 X 10-10 m/W is measured on the base of gain characteristics. An all-fiber Brillouin laser with the maximum unsaturated power of 54.6 mW at 1550 nm and a slope efficiency of 38.2% is achieved from a 200-m tellurite fiber by employing a ring cavity. Furthermore, widely tunable (~27 nm) Brillouin comb laser with 26 lines spaced at 7.97 GHz is obtained from the ring laser cavity including an erbium-doped fiber amplifier (EDFA). A simple theoretical model based on laser threshold theory successfully explains the properties of Brillouin comb lasers. Stimulated Brillouin scattering (SBS)-induced time delay per unit power and per unit length is also calculated using the measured data of Brillouin gain coefficients. A peak value of 0.09246 ns/mW/m and a time delay slope efficiency of 1.75 ns/dB are obtained for this tellurite fiber. Potential performance of a tellurite fiber for slow light generation is clarified on the base of Brillouin gain characteristic. Our results show that tellurite fiber is a promising gain medium for Brillouin fiber amplifiers, lasers, and slow light generation due to its low background loss and large Brillouin gain coefficient. View full abstract»

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  • Tunable Optical Delay Using Four-Wave Mixing in a 35-cm Highly Nonlinear Bismuth-Oxide Fiber and Group Velocity Dispersion

    Page(s): 499 - 504
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (478 KB) |  | HTML iconHTML  

    In this paper, an optically controlled tunable delay scheme has been proposed using four-wave mixing (FWM) wavelength conversion in a 35-cm highly nonlinear bismuth-oxide fiber (Bi-NLF) together with group velocity dispersion (GVD) in a chirped fiber Bragg grating (CFBG). The Bi-NLF offers a very large nonlinearity and gives rise to significant FWM over a short fiber segment. With the use of a CFBG, a delay range over 185 ps has been experimentally demonstrated. To investigate the performance of the tunable delay, we have applied the scheme for variable delays of 10-Gb/s amplitude-shift keying (ASK) and differential phase-shift keying (DPSK) data signals. The bit error rate (BER) measurements show a power penalty of less than 3.5 dB for both amplitude- and phase-modulated data formats. To further increase the delay time, the CFBG has been replaced by a dispersion compensated fiber (DCF) that provides a wider bandwidth of operation. A variable delay up to 840 ps has been obtained using dual-pump FWM that offers a conversion bandwidth of about 40 nm. The large conversion range helps to minimize GVD-induced pulse distortion as a shorter DCF can be used for a given delay. The Bi-NLF provides an enhanced stimulated Brillouin scattering (SBS) threshold, a reduced latency, and an increased compactness of the approach for practical applications. View full abstract»

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  • High-Performance Electroabsorption Modulators Utilizing Microwave Reflection Control Technique

    Page(s): 505 - 511
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    A microwave reflection control technique that improves the performance of electroabsorption modulators (EAMs) is presented. The technique exploits the superposition of incident and reflected electrical signals as a modulation signal to enhance the modulation signal voltage applied to EAMs and therefore differs from conventional impedance matching techniques in terms of operating principle. A nearly flat electrical-to-optical frequency response up to 50 GHz and significant improvement in eye openings at 40 Gbit/s have been achieved with the technique. The effects of the technique are demonstrated through both experimental and computational investigations. View full abstract»

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  • Investigation on Single-Mode–Multimode– Single-Mode Fiber Structure

    Page(s): 512 - 519
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (833 KB) |  | HTML iconHTML  

    This paper presents an investigation on a single-mode-multimode-single-mode fiber structure. A one-way guided-mode propagation analysis for the circular symmetry waveguide is employed to model the light propagation and the approximated formulations are derived and evaluated concerning the accuracy. Phase conjunction of the multimode interference within the fiber structure is revealed. A simple way to predict and analyze the spectral response of the structure is presented through the space to wavelength mapping with the derived approximated formulations. The prediction of spectral response is verified numerically and experimentally. View full abstract»

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  • Performance Evaluation of Single-Wavelength Fiber Delay Line Buffer With Finite Waiting Places

    Page(s): 520 - 527
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (660 KB) |  | HTML iconHTML  

    The performance of single-wavelength fiber delay line buffer with finite waiting places is evaluated in this paper. For Poisson arriving packets with arbitrarily distributed lengths, the generating function of delay time distribution can be derived from the quantized delay buffer model. Then queue length distributions, loss probability, and other important performance measures can be figured out. Specifically, two important cases of negative-exponentially distributed packet lengths and fixed packet lengths are considered and compared. The accuracy of the proposed approach is verified through simulation. It is also observed that the buffer system performs more effectively for the fixed-length packets. View full abstract»

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  • Full Vectorial 3-D Sensitivity Analysis and Design Optimization Using BPM

    Page(s): 528 - 536
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    We present a novel approach to the sensitivity analysis of 3D structures using the full vectorial beam propagation method (FVBPM). Using no extra simulations, the sensitivities of the response with respect to all design parameters are obtained regardless of their number. Our approach is exploited to calculate the sensitivities of the propagation constants of multimode waveguides. It is also applied to the 3D imaginary distance FVBPM (ID-FVBPM) and utilized to extract the sensitivities of the mode parameters. The calculated sensitivities are then utilized within a gradient-based optimization algorithm to illustrate the application of the obtained sensitivities. The accuracy of our approach is verified through a comparison with the expensive central finite difference applied directly at the response level. View full abstract»

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  • Multifiber Shared-Per-Wavelength All-Optical Switching: Architectures, Control, and Performance

    Page(s): 537 - 551
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    A new wavelength converter sharing strategy for multifiber optical switches, namely shared-per-wavelength (SPW), which employs wavelength converters with fixed input wavelengths is presented. The aim is to reduce switch costs by using simpler optical components and low complexity space switching matrices. Practical implementations of both the well-known shared-per-node (SPN) and the new SPW schemes are presented, as well as the related scheduling algorithms to manage optical packet forwarding in synchronous scenario. An analytical model to evaluate blocking performance of the SPN architecture is also provided. Results show the accuracy of the model in the range of interest for switch design. The proposed architectures are compared in terms of performance and number of optical components employed. The SPW approach is shown to save a large number of semiconductor optical amplifier gates with respect to the SPN one when the number of fibers per interface is suitably not too high. In these cases, the SPW architecture requires a number of wavelength converters higher than the SPN, but simpler, being their inputs tuned on a single wavelength. View full abstract»

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  • Design, Analysis and Experimental Testing of BPSK Homodyne Receivers Based on Subcarrier Optical Phase-Locked Loop

    Page(s): 552 - 559
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1008 KB) |  | HTML iconHTML  

    The analysis of a subcarrier optical phase-locked loop (SC-OPLL) is carried out in order to optimize phase-locking performance. A new parameters optimization procedure, useful for OPLL design, is demonstrated theoretically and experimentally. An SC-OPLL based on this procedure has been realized, so a pilot carrier SC-OPLL and a nonlinear SC-OPLL optical receiver have been experimentally constructed and tested. An 8B/10B line coding is employed for pilot carrier SC-OPLL receiver in order to improve performance and a new architecture of decision-driven PLL is experimentally demonstrated. View full abstract»

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  • A Novel Integrated Multistage 2-D MEMS Optical Switch With Spanke–Benes Architecture

    Page(s): 560 - 568
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    Due to the emergence of high-capacity wavelength-division multiplexing transmission systems, new optical cross-connect (OXC) architectures that make a large number of fiber/wavelength counts to switch the signal in the optical domain are needed. Optical microelectromechanical system (MEMS) switches are regarded as the most promising optical switch technology to achieve such functionalities. In this paper, we propose a novel integrated multistage two-dimensional (2-D) MEMS optical switch design with Spanke-Benes architecture and compare it with the conventional crossbar architecture, the L-switching architecture, and Shuffle-Benes architecture. Our proposed architecture is very suitable for building large-port-count 2-D MEMS switches and achieves much better performance in terms of beam divergence loss, longest optical path, mirror radius, substrate size, port-to-port repeatability, and power consumption than the other three architectures. Furthermore, compared with the 2-D conventional crossbar switch commercially available now, the proposed architecture can save 50% mirrors, shorten 87.5% longest optical path, minify 65% mirror radius, and shrink 90% substrate size. View full abstract»

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  • Asymmetric Tuning Schemes of MEMS Dual-Shutter VOA

    Page(s): 569 - 579
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    A dual-shutter MEMS variable optical attenuator (VOA) is designed for advanced tuning functions such as linear attenuation relationship and simultaneous coarse and fine tunings. The mechanism behind is to take advantage of the additional shutter to render one more degree of freedom for attenuation adjustment. Although dual-shutter VOAs with asymmetric functionalities have been reported before, these intrinsic capabilities owing to asymmetry have not been extensively investigated. In experiment, the fabricated VOA device has demonstrated a linear tuning over a 20-dB range with respect to the driving voltage of one shutter, and it has also realized simultaneously coarse tuning (2.5 dB/V) and fine tuning (0.1 dB/V) by the two shutters. Ideally, the tuning can start from any available working point, linear to any controlling parameter, at any slope of linearity, and with any tuning resolution. Theoretical attenuation model has also been developed to provide a roadmap for the VOA design and choice of working point. An interesting finding is that over a certain range the linear attenuation can be obtained by moving a fixed aperture rather than by reducing the aperture size, which greatly relaxes the difficulty of shutter position control. The measured results match well with the theoretical data, implying the possibility of developing a look-up table to locate the shutter positions quickly. The dual-shutter VOA accomplishes these features without the need of high-precision control systems and therefore gives a structure-based rather than a control-system-based solution, clearly advantageous over the previously developed VOAs. View full abstract»

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  • Numerical Simulations of an Optical Fiber Drawing Process Under Uncertainty

    Page(s): 580 - 587
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    Manufacture of optical fibers is subject to inherent uncertainty in various process and material parameters, which, in turn, leads to variability in product quality and impacts the reliability of the optical fibers in use. Analysis of the interactive effects of parameter uncertainty on the optical fiber quality is imperative in a robust-design endeavor. To this end, a methodology for simulation of optical fiber drawing process under uncertainty is presented by considering a two-dimensional (2D) numerical model of the flow, heat and mass transfer phenomena involved in the fiber drawing process. A sampling-based stochastic model is developed, and parametric analysis is presented to elucidate the effects of uncertainty in several process and material parameters on the variability of index of refraction, residual stress, maximum tension, and defect concentration. Design maps are derived from the analysis which provide for selection of furnace wall temperature as a function of the input parameter uncertainty and target maximum acceptable variability in the index of refraction, residual stress, maximum tension, and defects. View full abstract»

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  • Generation of a CW Local Oscillator Signal Using a Stabilized Injection Locked Semiconductor Laser

    Page(s): 588 - 599
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    We explore the technique of injection locking a semiconductor laser with a portion of the received optical signal to regenerate a local oscillator for eventual use with a homodyne receiver. In addition, we show that the injection locking process can be electronically stabilized by using the Modulation Transfer Ratio (MTR) of the slave laser as a monitor, given either a DFB or Fabry-Perot slave laser. We show that this stabilization technique maintains injection lock (given a locking range of ~1 GHz) for laser drift much greater than what is expected in a typical transmission system. In addition, we explore the quality of the output of the slave laser, and analyze its suitability as a local oscillator signal for a homodyne receiver. View full abstract»

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  • Assessment of Rational Approximations for Square Root Operator in Bidirectional Beam Propagation Method

    Page(s): 600 - 607
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    Accurate rational approximations to the square root operators are crucial for the bidirectional beam propagation method in simulation of strongly reflective structures. An assessment and comparison of various commonly used rational approximations is performed for both transverse electric (TE) and transverse magnetic (TM) waves. The range of validity and level of accuracy for the different approximations are studied by investigating the structures with varying reflection intensities. Guidelines for accurately modeling of evanescent and propagating modes are provided. View full abstract»

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  • InP-Based Mach–Zehnder Modulator With Capacitively Loaded Traveling-Wave Electrodes

    Page(s): 608 - 615
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    InP-based Mach-Zehnder modulators with capacitively loaded traveling-wave electrodes (CL-TWEs), which have segmented structures along the optical waveguides, are presented. Devices with various structural parameters for gap length (the length between adjacent segmented phase modulators) and total active length were fabricated and investigated both optically and electrically. Excellent characteristics such as characteristic impedance matching to 50 Omega and low electrical propagation losses were obtained. Using the optimum structures, 40- and 10-Gb/s large signal operations were successfully performed with peak-to-peak driving voltages of 3.0 and 1.2 V, respectively. The effects of structural parameters, such as gap length and total active length on electrical and optical modulation properties, are discussed. View full abstract»

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  • Distributed Protocol for Removal of Loop Backs and Optimum Allocation of p-Cycles to Minimize the Restored Path Lengths

    Page(s): 616 - 627
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    p-Cycle-based protection is one of the most promising techniques of span protection in optical networks because of mesh-like efficiency and ring-like speed. We have presented a modified distributed cycle preconfiguration protocol (MDCPC) which reduces the computational complexities, by finding all the copies of the same p-cycle in single iteration. All the copies of the same p-cycle are aggregated together to reduce the number of switching fabrics and the amount of signalling traffic. Further, the restoration paths provided by the p-cycles are usually many hops long, as longer p-cycles provide better efficiency. Obviously, with longer p-cycles, the nodes in the working path may be repeated in the restoration path provided by the p-cycle. They will give rise to loop backs in the restored path. The restored path lengths will unnecessarily be longer due to these loop backs. If these loop backs can be removed, the restored path length will be reduced significantly, and redundant capacity will also be released. In the present work, a distributed protocol has been presented for the implementation of removal of loop back (RLB) algorithm to reconfigure the restored path. The reduction in the restored path length also depends on the fact that which p-cycle is being used to protect a particular path. The problem has been formulated as optimum p-cycle allocation (OPA) problem and solved with the Hungarian algorithm. The average lengths of the restored paths with and without RLB for the networks with 2.0 average nodal degree have also been derived. View full abstract»

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  • Generation of Power-Efficient FCC-Compliant UWB Waveforms Using FBGs: Analysis and Experiment

    Page(s): 628 - 635
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    In this paper, we design, analyze, and demonstrate experimentally U.S. Federal Communications Commission (FCC)- compliant power-efficient ultrawideband (UWB) waveforms generated by optical pulse shaping. The time-domain pulse shape is written in the frequency domain, and a single-mode fiber performs the frequency-to-time conversion. The waveform is inscribed in the frequency domain by the fiber Bragg grating (FBG). A significant challenge for this approach is elimination of an unwanted, positive rectangular pulse superimposed on the desired waveform. Our innovative use of balanced photodetection eliminates this pedestal, assuring compliance with the FCC mask at low frequency. Three UWB pulses with duration of 0.3,0.6, and 1.2 ns are designed and tested experimentally. Whereas an excellent match between the optimized and measured pulses is achieved for the simpler, shorter duration waveforms, the noise in the fabrication process of FBGs limits the generation of the more complex, longer duration waveforms. View full abstract»

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  • Quality without compromise [advertisement]

    Page(s): 636
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  • IEEE copyright form

    Page(s): 637 - 638
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  • Journal of Lightwave Technology Information for authors

    Page(s): 639
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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