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Lightwave Technology, Journal of

Issue 8 • Date Aug. 2004

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Displaying Results 1 - 25 of 30
  • [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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  • Table of contents

    Page(s): 1833
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  • Sensitivity evaluation of baseband carrier-sense circuit for optical CSMA/CA packet networks

    Page(s): 1834 - 1843
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (608 KB) |  | HTML iconHTML  

    The ability to detect the presence or absence of optical signals on specific channels is used to prevent packet collisions in networks implementing the optical carrier-sense multiple-access with collision avoidance (CSMA/CA) protocol. This optical carrier-sense capability can be provided by a baseband carrier-sense circuit (BCSC), which directly detects the envelope of optical packets propagating in the network. A fraction of the optical power of packets passing through a node is tapped off for detection at the BCSC. It is therefore desirable to minimize the amount of optical power required at the circuit to perform reliable packet detection such that the additional insertion loss encountered by the in-transit packets is minimal. However, the performance of the BCSC is limited at low levels of received optical power. For a given topology and size of a practical optical CSMA/CA packet network, knowledge of this sensitivity limit is essential for determining the power budget while ensuring that collision avoidance and minimal insertion loss are achieved. This paper identifies the factors that contribute to the sensitivity of the BCSC. A theoretical description of a practical implementation of the BCSC is derived and an efficient method to evaluate the sensitivity is presented. The theory is validated using experiments, with results showing that the model presented in this paper is a useful tool for the design and performance analysis of highly sensitive BCSCs in future optical CSMA/CA networks. View full abstract»

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  • An optimal feedforward design for complete PMD compensation up to the second order

    Page(s): 1844 - 1847
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    As an extension to a previous paper, this paper describes the optimization of a second-order, feedforward polarization-mode dispersion (PMD) compensation scheme by reducing its degrees of freedom (DOF) by two. The new design is optimal in the sense that the number of DOF used is the same as the minimal number of DOF required. Also derived is a set of constraint equations that govern the choice of various system parameters. View full abstract»

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  • Long-term monitoring of polarization-mode dispersion of aerial optical cables with respect to line availability

    Page(s): 1848 - 1855
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (352 KB) |  | HTML iconHTML  

    Physical and technical limits become important when trying to increase data transfer rates to tens of gigabits and higher for already installed optical cables. Polarization-mode dispersion (PMD) is one of the crucial transmission constraints, especially for aerial cables exposed to environmental stresses. Optical fibers in the laboratory and three aerial optical fiber cable links across the Swiss alps were characterized with respect to PMD. Long-term measurement results are correlated to weather data along the cables, and predictions regarding line availability are made. View full abstract»

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  • Signal-to-noise-ratio degradation caused by polarization-dependent loss and the effect of dynamic gain equalization

    Page(s): 1856 - 1871
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    This paper describes a study of the effect of polarization-dependent loss (PDL) on the signal-to-noise ratio (SNR) in optical communications systems, taking into account the effect of dynamic gain equalization. The paper shows that the PDL-induced SNR penalty is caused by two distinct mechanisms related to the two polarization components of the amplified spontaneous emission noise generated in each amplifier. The noise components whose polarization is parallel to the signal at the various amplifier locations dominate the PDL-induced penalty in the absence of gain equalization. In the presence of even a moderate number of gain equalizers, the orthogonal noise components dominate the SNR degradation. Expressions are obtained relating the outage probability to the necessary performance margin that needs to be allocated for PDL. View full abstract»

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  • Optimal choice of compensation PMD vector in feedforward-type second-order PMD compensation

    Page(s): 1872 - 1876
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (152 KB) |  | HTML iconHTML  

    In this paper, the formula of an optimal compensation vector, which is defined as an input polarization-mode dispersion (PMD) vector of the compensator, for second-order PMD compensation has been derived from the minimization of the root-mean-square (rms) pulse-broadening factor. The derived optimal compensation vector is a linear combination of frequency-averaged PMD vectors and output states of polarization, which shows a similar trend to the previously reported optimal first-order PMD compensation. The rms pulse-broadening factor after optimal second-order PMD compensation has been semianalytically calculated and compared with the previously reported simulation result. They are in good agreement. The formula of the optimal second-order compensation vector derived in this paper provides indispensable information for feedforward second-order PMD compensation. View full abstract»

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  • Compensation of intrachannel effects in symmetric dispersion-managed transmission systems

    Page(s): 1877 - 1882
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    This paper analyzes perturbations caused by nonlinear intrachannel effects and shows how to cancel them by symmetric configuration of transmission and dispersion-compensating fiber. From an analytical study of amplitude and timing jitter conditions are derived to reduce them effectively. Simulations are performed using different schemes of dispersion compensation and improvement and limits of regenerative symmetric links are also discussed. Finally, the paper presents a simple fiber-based configuration to reduce timing jitter in particular. The quality of existing transmission systems is improved. View full abstract»

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  • Tuning technique to optimize input power of a cross-phase modulation wavelength converter

    Page(s): 1883 - 1892
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    This paper proposes a tuning technique to optimize the input power of a cross-phase modulation wavelength converter (XPM-WC). The focus is on an output signal whose wavelength is the same as the input signal. The optimum input power can be easily set by keeping the output signal (not converted signal) power constant. Input continuous-wave (CW) power should be increased or decreased with increasing or decreasing input signal power so that the output signal power stays fixed at the optimum level. Observing the eye pattern of the converted signal is unnecessary. Wavelength conversion from a fixed optical channel to a random one (30 channels with 100-GHz spacing) is successfully demonstrated by using this technique. A low-power penalty (<1dB) and a low-power fluctuation (<1dB) were confirmed in all optical channels. An XPM-WC unit containing a variable CW light source and its level controller were fabricated and simultaneous and automatic operation was confirmed. View full abstract»

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  • Evaluation on system outage probability due to temperature variation and statistically distributed chromatic dispersion of optical fiber

    Page(s): 1893 - 1898
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    This paper discusses the evaluation of the system outage probability caused by the temperature variation and statistically distributed chromatic dispersion of optical fiber in a high-speed (>40 Gb/s) optical network. This was to identify when the tunable dispersion compensator should be used at every channel. View full abstract»

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  • Design of double-pass dispersion-compensated Raman amplifiers for improved efficiency: guidelines and optimizations

    Page(s): 1899 - 1908
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    In this paper, an intensive theoretical and experimental investigation is conducted on the dispersion-compensating Raman amplification module configured in double-pass geometry. An analytical model is developed to study the gain/pump efficiency improvement and the noise performance in a novel double-pass discrete-Raman-amplifier (DCRA) system. This paper demonstrates that the gain and pump efficiency can be improved significantly by using the double-pass configuration and the pump light reflector. The impairments of multipath-interference (MPI) noise due to the Rayleigh scattering and the external reflection are analyzed in order to balance the high gain efficiency and the enhanced MPI noise in the double-pass DCRA. Furthermore, the nonlinear penalty in the DCRA system is investigated and a 10-Gb/s nonreturn-to-zero (NRZ) signal transmission in a 4 × 100-km fiber system is simulated. The signal quality and bit-error rate are examined, and the optimization is done with reference to the input signal level and Raman gain; hence, the impact of double-pass DCRA on the dispersion-compensated optical communication systems is explored. View full abstract»

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  • Analysis of dispersion properties in hexagonal hollow fiber

    Page(s): 1909 - 1914
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    A hollow fiber with new cross section is studied by means of a numerical simulator for modal analysis based on the finite-difference time-domain method (FDTD). Results show that light can be confined into the core area due to six right angles of the hexagonal glass with high index, and the peak intensity is located in the low-index air region. Distribution of the transverse electric-field intensity as well as dispersion properties of the fundamental mode are given. View full abstract»

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  • γ-rays and pulsed X-ray radiation responses of germanosilicate single-mode optical fibers: influence of cladding codopants

    Page(s): 1915 - 1922
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    The radiation-induced attenuation (RIA) in germanosilicate single-mode optical fibers was measured at 1.55 and 1.31 mm after a pulsed X-ray irradiation and at 1.55 mm during and after a steady-state g-ray irradiation. The influence of codoping the fiber cladding with germanium (Ge), phosphorus (P), and fluorine (F) on the sensitivity of Ge-doped core fibers was characterized. P-codoping makes it possible to decrease the RIA for short times (10*6 s*10*3 s) post- pulse. However, P-codoped fibers exhibit larger values of permanent RIA than P-free fibers after transient exposure and are inadequate for a steady-state environment. The impact of F-codoping depends on the other codopants incorporated in the fiber cladding, but its addition seems to be deleterious for the radiation hardening of the germanosilicate fiber at the two tested wavelengths. Ge-codoping increases the sensitivity of P-, F-codoped fibers under X-rays and steady-state g-ray irradiation, whereas it decreases the RIA in F-doped ones. Some hypotheses on the creation mechanisms and properties of the color centers related to these three codopants are proposed. View full abstract»

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  • The single-mode condition for silicon-on-insulator optical rib waveguides with large cross section

    Page(s): 1923 - 1929
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    Results from detailed numerical analyses of the modal characteristics of large-cross-section silicon-on-insulator-based rib waveguides are presented. They highlight for the first time that satisfying widely used design criteria is not sufficient to ensure single-mode behavior. In particular, the geometries that the design formulas predict should be single-mode are shown to support higher order vertical modes that do not couple (leak) into the outer slab region and are thus low loss in nature. Fortunately, a wide range of practical rib geometries still remains for which the leakage loss of modes other than those of EH00 and HE00 is sufficiently high to make the waveguides effectively single mode for each polarization. View full abstract»

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  • Optical circular-polarization modulator employing tilt-poled electrooptic polymers

    Page(s): 1930 - 1934
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    A polymer-based integrated circular-polarization modulator (CPM) is demonstrated in this paper. Tilted poling is adopted to achieve polarization conversion in the electrooptic (EO) polymeric waveguide and then realize the power balance between transverse electric and transverse magnetic modes. Detailed analysis and experiments on polarization conversion are presented. The tensor nature of poled polymeric materials is used to generate the phase difference. Contact poling is applied to perform tilted poling and activate the EO effect of polymeric materials. With appropriate voltage control, the polarization state of the output from the CPM can alternate between the left and right-hand-circular states. The extinction ratios at the 45°- and -45°-tilted linearly polarized states are larger than 25 dB. View full abstract»

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  • Evaluation of amplitude-stabilized optical pulse trains from rational harmonically mode-locked fiber ring lasers

    Page(s): 1935 - 1945
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    This paper investigates rational harmonically mode-locked fiber ring lasers generating amplitude-stabilized fourth-order optical pulse trains at 13.91 GHz using a modulation signal frequency of 3.477 GHz. Pulse amplitude stabilization in terms of both amplitude equality and low amplitude noise is realized by using the nonlinear characteristics of a Mach-Zehnder intensity modulator in conjunction with intracavity optical filtering. The generated optical pulse trains are investigated for their amplitude equalization, amplitude noise, supermode noise suppression, and pulse timing jitter. It is shown that the pulses remained close to transform-limited over an operating wavelength range of 1535-1565 nm. View full abstract»

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  • Multichannel amplification in strongly pumped EDFAs

    Page(s): 1946 - 1952
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    Multichannel erbium-doped fiber amplifiers (EDFAs) are analyzed based on a rate-equation model. Forward pumping is considered and amplified spontaneous emission (ASE) as well as scattering loss are taken into account. An analytical approximation to calculate the amplification in high-power multichannel EDFAs is also introduced in this paper. Results for both the numerical and approximate analytical models are derived and discussed. It is shown that under the considered conditions, the analytical solutions provide a good approximation to the exact numerical solution and thus may be used for the design of such amplifiers. View full abstract»

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  • Characterization of the jitter in a mode-locked Er-fiber laser and its application in photonic sampling for analog-to-digital conversion at 10 gsample/s

    Page(s): 1953 - 1961
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    This paper compares two approaches for evaluating the amplitude and timing jitters of an Er-fiber laser mode-locked at 10 GHz. Using a low-noise oscillator as the clock drive for the mode-locking, relative amplitude jitter was measured as low as 0.0384% and timing jitter as low as 0.0153% (Δf=100 Hz-40 MHz). Applying the mode-locked pulse train in a photonic sampling experiment at 10 Gsample/s, a spurious free dynamic range (SFDR) of ∼48.5 dB (over the Nyquist bandwidth of 5 GHz) for multiple analog inputs at L band (1-2.6 GHz). These results correspond to an analog-to-digital conversion resolution of ∼8 SFDR bits at 10 Gsample/s. Finally, the use of "instantaneous companding" is demonstrated to correct for third-order distortions generated by a Mach-Zehnder modulator used in the photonic sampling link. View full abstract»

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  • Design of distributed Bragg reflector structures for transverse-mode discrimination in vertical-cavity surface-emitting lasers

    Page(s): 1962 - 1967
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    An angular spectrum of plane-wave representation is employed to calculate the discrimination between the fundamental and higher order transverse modes in step-index-guided vertical-cavity surface-emitting lasers. The effect of material composition and number of layer pairs in the distributed Bragg reflectors, as well as mode size and structure, are examined with the goal of optimizing the mode discrimination for better mode stability and higher single-mode power. In particular, it is shown that decreasing the width of the distributed Bragg reflector stopband, by means of controlling the material composition, improves significantly the mode discrimination. View full abstract»

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  • Tunable notch filter using a thermooptic long-period grating

    Page(s): 1968 - 1975
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    This paper proposes a tunable notch filter using a thermooptic long-period grating and investigates it theoretically. This notch filter is in the form of an integrated optical device and is based on a simple structure as compared with existing integrated optical notch filters. The thermooptic grating denotes a thermooptic index perturbation induced by periodic heaters. The attenuation of a resonance band in the transmission spectrum of the proposed notch filter can be controlled by adjusting the electric power applied to the periodic heaters. Employing the heat transfer theory and the coupled-mode theory, the proposed filter is designed and analyzed. The paper also presents analytic expressions for the temperature change due to a heater and the coupling coefficients due to the thermooptic grating. This filter may have potential as a compact dynamically controllable device like a tunable gain flattening filter. View full abstract»

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  • Synthesis of long-period fiber gratings with the inverted erbium gain spectrum using the multiport lattice filter model

    Page(s): 1976 - 1986
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1072 KB) |  | HTML iconHTML  

    This paper proposes an accurate modeling technique of concatenated long-period fiber gratings (LPFGs). The proposed technique is then applied to the synthesis of LPFGs for the erbium gain equalization using both the simulated annealing and the steepest descent minimization technique. A piecewise-uniform LPFG is theoretically synthesized according to the inverted gain spectrum of a commercially available erbium-doped fiber amplifier (EDFA) over the range of 1525-1570 nm. Sensitivity analysis of the designed structure is presented by Monte Carlo simulation with regard to the manufactured amplitude mask. To verify a synthesizing technique using the proposed modeling, the piecewise-uniform LPFGs for gain flattening of EDFA are fabricated and their spectra are also presented experimentally. View full abstract»

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  • Double-Layer antireflection coating design for semi-infinite one-dimensional photonic Crystals

    Page(s): 1987 - 1989
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    A theoretical formalism is established for double-layer (DL) antireflection coating (ARC) on a one-dimensional (1-D) photonic crystal (PC). Conventional DL-ARC for a bulk is equally applicable for a 1-D PC when the bulk substrate index is replaced with the optical admittance, which can be obtained from the electromagnetic Bloch waves of the infinite 1-D PC. Numerical calculations are performed for a model structure composed of GaAs and AlAs-oxide layers to confirm the validity of the theory. In terms of realization and practicality, this DL-ARC is expected to be superior to the single-layer version. View full abstract»

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  • Accelerated-aging studies of chirped Bragg gratings written in deuterium-loaded Germano-silicate fibers

    Page(s): 1990 - 2000
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    Accelerated-aging studies of chirped Bragg gratings written in deuterium-loaded germano-silicate fibers were carried out using isothermal and continuous isochronal anneal methods. The master aging curve obtained from the isothermal decay is explained using the Arrhenius-rate-model-based equation. An empirical polynomial function was used to fit the continuous isochronal anneal data. The estimated attempt frequency (n) values from the two anneal methods were found to agree well within error. Further, the model-based calculations were found to predict postanneal long-term behavior of the gratings extremely well. Implications of the two anneal methods to accurately predict the thermal stability of chirped fiber Bragg gratings are discussed in light of rapid and reliable qualification of different types of gratings written in different fibers. View full abstract»

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  • Analysis and development of a tunable fiber Bragg grating filter based on axial tension/compression

    Page(s): 2001 - 2013
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    A tunable optical filter based on the axial strain of the fiber Bragg grating (FBG) is discussed. A wavelength range of 46 nm in compression and 10.5 nm in tension with negligible variations in reflectivity and bandwidth of the central Bragg wavelength reflectivity peak were obtained. The device consists of two fixed ferrules and one guiding ferrule. The difficulties with compressing the FBG were handled by carefully selecting tolerances and adjustment procedures. The device allows both tension and compression of FBG and the use of different FBG lengths and actuators. The effects of glue deformation and bending of the FBG during compression are analyzed in detail. 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.

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