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Lightwave Technology, Journal of

Issue 10 • Date Oct. 2000

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Displaying Results 1 - 15 of 15
  • Optical beat noise suppression and power equalization in subcarrier multiple access passive optical networks by downstream feedback

    Page(s): 1337 - 1347
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (308 KB)  

    This paper describes a cost-effective method of suppressing optical beat noise in subcarrier multiple access passive optical networks. The method is based on initial power equalization followed by automatic fine tuning of laser wavelengths, via downstream feedback control of their mean powers, so that the receiver noise floor level is continuously minimized. Application and performance of the method is demonstrated for a low-cost 16-channel system with uncooled Fabry-Perot lasers, utilizing narrow-band QPSK modulated subcarrier frequencies over more than one octave. In static and dynamic temperature worst-case situations a considerable reduction in the number of transmission errors caused by optical beat noise is observed, depending on the temperature change rate. View full abstract»

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  • Error statistics of 64-QAM signal in AM/64-QAM hybrid optical transmission

    Page(s): 1348 - 1354
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (139 KB)  

    This paper describes the performance of an error correction system based on the DAVIC specifications. It also presents an error statistics property and its analytical model for the impulse noise induced by clipping in amplitude modulation (AM)/64 quadrature amplitude modulation (QAM) hybrid optical transmission (hybrid transmission). We found in hybrid transmission that the errors cannot be completely corrected by the error correction of DAVIC after hit error rate (BER) measurement with error correction, and then the error statistics of the 64-QAM channel were evaluated. It was confirmed that errors occasionally occur in long bursts that exceed an interleaver block length of the error correction when the impulse noise degrades the 64-QAM signal's BER. We believe that the error burst is caused by the slowed fluctuation of the envelope of a frequency division multiplex (FDM) signal in hybrid transmission. Once a portion of the envelope amplitude reaches the clipping level, the duration of maintaining such a condition is much longer than the 64-QAM symbol time. Accordingly, the errors occasionally run for more than 100 symbols. We apply Rice's fading duration distribution model to explain this error burst occurrence mechanism and its statistical manner and discuss this model's validity by comparison between the theoretical and measurement data of error statistics property. Consequently, we found that the theoretical value by the proposed model is in excellent agreement with the measurement data and confirmed that the proposed model is valid for analyzing the error manner for the clipping induced error. View full abstract»

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  • Millimeter-wave broad-band fiber-wireless system incorporating baseband data transmission over fiber and remote LO delivery

    Page(s): 1355 - 1363
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (164 KB)  

    We present the first demonstration of a millimeter-wave (mm-wave) broadband fiber-wireless system which incorporates baseband data transmission in both the downstream (622 Mb/s) and upstream (155 Mb/s) directions. The local oscillator (LO) required at the remote antenna base station for up- and downconversion to/from the mm-wave radio frequency (RF) is delivered remotely via a modulation scheme that is tolerant to the effects of fiber chromatic dispersion on the detected LO carrier power. The technique employs a single dual electrode modulator located at the central office (CO) and the data and an RF signal at a frequency equal to half the LO frequency, are applied simultaneously to the device. The modulation scheme was optimized as a function of the modulator operating conditions. Simultaneous bidirectional radio transmission in the mm-wave fiber-wireless network was implemented using specially designed mm-wave diplexers located at the base station (BS) and customer unit, and a single Ka-band printed antenna array at the BS operating simultaneously in transmit and receive mode. Error-free data transmission was demonstrated for both down(34.8 GHz) and uplinks (37.5 GHz) after 20 km of single-mode optical fiber and a bit error rate (BER) of 10/sup -6/ was achieved after the inclusion of a 2-m radio link. View full abstract»

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  • 40-Gb/s RZ transmission over a transoceanic distance in a dispersion managed standard fiber using a modified inline synchronous modulation method

    Page(s): 1364 - 1373
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (238 KB)  

    This paper analyzes in detail numerically a 40-Gb/s return-to-zero (RZ) transmission system over a transoceanic distance in a strongly dispersion managed line composed of standard single-mode fiber (SMF) and dispersion compensation fiber (DCF). We derived a periodically steady-state pulse (a DM soliton) in a DM line. Since the pulse width of a steady-state pulse is too broad for a 40 Gb/s system, the conventional in-line synchronous modulation technique cannot greatly improve the transmission quality. However, we found that the modified inline synchronous modulation technique, which is reported as the black-box optical regenerator, can effectively extend the transmission distance even in such a strongly DM line. We discuss the mechanism of the modified synchronous modulation technique with respect to a steady-state pulse in a transmission line, and show that a 40-Gb/s RZ signal can be transmitted over 20 000 km. View full abstract»

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  • Mitigation of polarization-mode dispersion in optical multichannel systems

    Page(s): 1374 - 1380
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (129 KB)  

    Simulations of first-order polarization-mode dispersion (PMD) mitigation, based on the electrical power spectrum has been performed. We show that, although first-order compensation significantly improves the signal quality for PMD values of a few tenths of the bit-slot, the improvement still is deficient for telecom purposes when the PMD value neighbors a third of the bit-slot. We, therefore, propose and analyze a novel concept for PMD mitigation in optical multichannel systems, which increases the systems reliability at the expense of the total capacity for the same system. With the proposed method, which uses switching to redundant channels based on measurements of signal quality of all channels in the actual system, the PMD value can be increased to a half of the bit-slot while still keeping the probability for signal outage at acceptable low levels. In the appendixes we simulate the statistical impact of different PMD-emulator models and we show that static bit sequences may induce notches in the electrical power spectrum. These notches may obstruct the extraction of feedback signals for PMD-mitigator schemes based on electrical power spectrum. View full abstract»

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  • A novel in-service measurement technique using the same wavelength band as SCM signals

    Page(s): 1381 - 1388
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (177 KB)  

    This paper proposes a new technique for measuring in-service optical fibers, that uses an optical time domain reflectometer (OTDR). The feature of the proposed technique is that the OTDR light is in the same wavelength band as the video signal, which is distributed by using the subcarrier multiplexing (SCM) technique. In a 40-channel SCM system operating at a signal wavelength of 1.558 /spl mu/m, we show that the required video quality can be maintained, by using the proposed OTDR operating in the 1.55 /spl mu/m band, even though the measured fiber is in service and the OTDR light enters an optical receiver. Moreover, we clarify the conditions for undertaking measurements, without the need for optical filters designed to prevent OTDR light from degrading the SCM signal quality. View full abstract»

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  • Measurement of local beat length and differential group delay in installed single-mode fibers

    Page(s): 1389 - 1394
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (126 KB)  

    We present beat length and polarization mode dispersion (PMD) measurements performed on installed fibers. Results regard three different kinds of fibers: standard step index, dispersion shifted and nonzero dispersion (NZD). After a historical comparison with standard differential group delay measurement collected four years ago on the same fibers, we perform a spatial-resolved measurement of the beat length by analyzing the state of polarization of the backscattered field. We compare PMD properties of different fibers and calculate the statistical distribution of the beat length. The differential group delay (DGD) and the beat length statistics depend strongly on fiber type and on fiber position along the link. The influence of the beat length on the DGD is also discussed. View full abstract»

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  • Very large temperature-induced absorptive loss in high Te-containing chalcogenide fibers

    Page(s): 1395 - 1401
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (163 KB)  

    The change in the absorption loss relative to room temperature of the infrared (IR)-transmitting Ge/sub 15/As/sub 35/Se/sub (50-x)/Te/sub x/ glass fibers in the temperature range of -110/spl deg/C/spl les/T/spl les/110/spl deg/C was investigated. The attenuation increased significantly at T/spl ges/40/spl deg/C. This is mainly attributed to thermally activated free carriers associated with the semimetallic character of the Te atom. For /spl lambda//spl les/4.2 /spl mu/m, the loss due to electronic and free-carrier absorption was strongly affected by temperature. In the wavelength region of 5-11 /spl mu/m, the loss was mainly due to free-carrier absorption. Beyond /spl lambda//spl ges/11 /spl mu/m, multiphonon absorption dominated the loss spectrum at T/spl les/60/spl deg/C while free-carrier absorption contributed mainly to the total loss at T/spl ges/80/spl deg/C. View full abstract»

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  • Design and fabrication of silicon photonic crystal optical waveguides

    Page(s): 1402 - 1411
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (309 KB)  

    We have designed and fabricated waveguides that incorporate two-dimensional (2-D) photonic crystal geometry for lateral confinement of light, and total internal reflection for vertical confinement. Both square and triangular photonic crystal lattices were analyzed. A three-dimensional (3-D) finite-difference time-domain (FDTD) analysis was used to find design parameters of the photonic crystal and to calculate dispersion relations for the guided modes in the waveguide structure. We have developed a new fabrication technique to define these waveguides into silicon-on-insulator material. The waveguides are suspended in air in order to improve confinement in the vertical direction and symmetry properties of the structure. High-resolution fabrication allowed us to include different types of bends and optical cavities within the waveguides. View full abstract»

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  • Refractive-index profiling of graded-index planar waveguides from effective indexes measured with different external refractive indexes

    Page(s): 1412 - 1417
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (109 KB)  

    We extend the well-known inverse Wentzel-Kramer-Brillouin (WKB) method for refractive-index profiling of graded-index planar waveguides. We demonstrate, with numerical examples and experimental results, that the refractive-index profile of a graded-index planar waveguide can be calculated from effective indexes measured with different external refractive indexes. With this technique, single-mode and two-mode waveguides can be profiled easily to a good accuracy. View full abstract»

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  • Integrated tunable fiber gratings for dispersion management in high-bit rate systems

    Page(s): 1418 - 1432
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (330 KB)  

    Dispersion management is becoming paramount in high-speed wavelength-division-multiplexed lightwave systems, that operate at per-channel rates of 40 Gb/s and higher. The dispersion tolerances, in these systems, are small enough that sources of dispersion variation, that are negligible in slower systems, become critically important to network performance. At these high-bit rates, active dispersion compensation modules may be required to respond dynamically to changes occurring in the network, such as variations in the per-channel power, reconfigurations of the channel's path that are caused by add-drop operations, and environmental changes, such as changes in ambient temperature. We present a comprehensive discussion of an emerging tunable dispersion compensating device, based on thermally actuated fiber gratings. These per-channel devices rely on a distributed on-fiber thin film heater, deposited onto the outer surface of a fiber Bragg grating. Current flowing through the thin film generates resistive heating at rates that are governed by the thickness profile of the metal film. A chirp in the grating is obtained by using a thin-film, whose thickness varies with position along the length of the grating in a prescribed manner; the chirp rate is adjusted by varying the applied current. The paper reviews some of the basic characteristics of these devices and their implementation, in a range of different applications, including the mitigation of power penalties associated with optical power variations. We present detailed analysis of the impact of group-delay ripple and polarization-mode dispersion on systems performance, and present results from systems experiments, that demonstrate the performance of these devices at bit rates of 10, 20, 40 and 160 Gb/s. We also discuss advantages and disadvantages of this technology, and compare to other devices. View full abstract»

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  • The RPS method applied to the numerical solution of multimode slab waveguides with complex indexes

    Page(s): 1433 - 1436
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    In order to obtain the numerical solution of multimode slab waveguides with complex indexes, we propose a method named RPS, which integrates real index numerical method, perturbation method and shooting method. This RPS method avoids searching the solution in the whole complex plane, meanwhile, it is simple, fast and precise. The application shows that the RPS method is suitable for both the transverse electric (TE) and the transverse magnetic (TM) mode. View full abstract»

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  • A model for optoelectronically interconnected smart pixel arrays

    Page(s): 1437 - 1444
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (146 KB)  

    Theoretical results for modeling source-based smart pixel arrays are presented. Attention is focused on modeling the nonlinearities in sources, as well as electrical and optical couplings and interactions within a single pixel. A matrix formalism is used to generalize the theory to include the behavior of an entire smart pixel array consisting of interacting pixels with arbitrary optical and electrical interconnections. A vertical cavity surface emitting laser (VCSEL)-based smart pixel array is used for experimental demonstration of the application of the theory in the design and implementation of an optoelectronic flip-flop, where the nonlinear characteristics of the VCSELs are utilized in a positive feedback scheme to achieve bistability. View full abstract»

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  • A versatile method for analyzing paraxial optical propagation in dielectric structures

    Page(s): 1445 - 1452
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (202 KB)  

    This paper presents a fast and accurate quasi-analytic model for studying optical field propagation in weakly guiding dielectric structures. The proposed efficient and versatile computational scheme is obtained by merging the Hermite-Gauss (HG) total field expansion with the numerical collocation method and is particularly suited for longitudinally nonuniform structures. By means of a quasilinearization scheme, the same procedure has also been successfully applied to the analysis of field propagation in Kerr-nonlinear media. The latter achievement gives an indication of the great potentialities offered by this straight forward method. Several examples are discussed in the paper and in all cases the results computed by the proposed method favorably compare with those from alternative methods. View full abstract»

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  • A performance analysis of all-optical clock extraction circuit based on stimulated Brillouin scattering

    Page(s): 1453 - 1466
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (349 KB)  

    In this paper, we develop an analytical method to deal with the timing performance in an optical clock extraction circuit based on stimulated Brillouin scattering (SBS). Three kinds of SBS active filters are considered and their frequency-transfer functions are obtained under the assumption that pump depletion caused by SBS is negligible. When pump depletion is taken into account, an SBS active filter acts as a nonlinear filter. To investigate the timing performance at this situation, we introduce the concept of "dynamic frequency-transfer function" to describe its frequency-response property for a fixed-signal light and pump light. Using the obtained "frequency-transfer function," we give analytical expressions for both root-mean-square (rms) phase jitter and rms amplitude jitter of the extracted optical clock, in which we have taken the impacts of SBS gain, pump light linewidth, optical pulse chirp, and pump detuning into account. Finally, a detailed numerical investigation on the timing performance for the three active filters is presented. 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