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Lightwave Technology, Journal of

Issue 7 • Date July 2002

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Displaying Results 1 - 19 of 19
  • The channel capacity of a multispan DWDM system employing dispersive nonlinear optical fibers and an ideal coherent optical receiver

    Page(s): 1095 - 1101
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (303 KB) |  | HTML iconHTML  

    We present channel capacity calculations for a multispan dense wavelength division multiplexed (DWDM) system that employs an ideal coherent optical receiver. Both dispersive and dispersion-free single-mode nonlinear optical fibers are considered. Degradation due to interference among Kerr nonlinear noise and optical amplifier noise accumulated along many spans is included in our model calculations. We will show that in the low-power quasi--linear regime, a multispan system can be approximated by an "equivalent" single-span system. The "equivalent" Kerr coefficient for most dispersive fibers is shown to increase with the square root of the number of spans, in contrast to the linear scaling dependence for a dispersion-free fiber. For a conventional fiber with β = -20 ps2/km, our calculated capacity of 10 (2 x 80 km), 8 (8 x 80 km), and 6 (32 x 80 km) bps/Hz indicates that today's technologies with 0.4 bps/Hz have only realized 5% of the theoretical total capacity. We have shown an increased (or decreased) capacity by about 1 bps/Hz per ten-fold increase (decrease) in dispersion. View full abstract»

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  • Berenger and leaky modes in optical fibers terminated with a perfectly matched layer

    Page(s): 1141 - 1148
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (350 KB) |  | HTML iconHTML  

    Recently, it has been demonstrated that some field problems involving optical fibers can be solved more easily by enclosing the fiber with a perfectly matched layer (PML). In this paper, we investigate the dispersion relation for the transverse electric (TE), transverse magnetic (TM), and hybrid modes of such a fiber-PML combination. Within a good approximation, two types of modes can be distinguished: the leaky type, only depending on the fiber characteristics, and the so-called Berenger type, mainly depending on the PML characteristics. Analytical expressions for the propagation constants of the higher order modes are derived and compared with the exact values for two relevant examples: a vertical cavity surface emitting laser (VCSEL) cavity and a monomode fiber. View full abstract»

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  • Polymeric optical spot-size transformer with vertical and lateral tapers

    Page(s): 1188 - 1197
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (464 KB) |  | HTML iconHTML  

    The design, fabrication, and characterization of a polymeric optical spot-size transformer with vertical and lateral tapers is reported. The vertical taper is formed by utilizing the planarization properties of a polymer, while the lateral taper is defined by photolithography. An optimization method for the taper shape is described based on fundamental results from coupled local mode theory. A total fiber to waveguide insertion loss of 0.6 dB has been measured with the integration of the transformer, an improvement of 2.1 dB. The spatial alignment tolerance for 1 dB excess loss was measured to ±2.7μm, consistent with theory. View full abstract»

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  • Improved 60° bend transmission of submicron-width waveguides defined in two-dimensional photonic crystals

    Page(s): 1198 - 1203
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (338 KB) |  | HTML iconHTML  

    We compare quantitatively the transmission properties of various 60° bends carved into a photonic crystal based on a two-dimensional triangular lattice of holes perforating a GaAs-based heterostructure. The bends are inserted into channel waveguides defined by three missing rows in the photonic crystal. Their design is inspired by some ideas from classical integrated optics. We show experimentally that in some cases the transmission of the bent waveguide is fairly high, up to 70%, within a bandwidth of 3%, e.g., 30 nm at 1 μm, sufficient to contemplate wavelength-division-multiplexing applications. The observed performance opens the opportunity to implement a variety of optical functions in view of future photonic crystal integrated circuits for which low-loss bends constitute an essential building block. View full abstract»

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  • A high-efficiency nonlinear frequency converter with a built-in amplitude modulator

    Page(s): 1165 - 1172
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (371 KB) |  | HTML iconHTML  

    We report simultaneous frequency conversion and amplitude modulation in an optical second-harmonic generator by electrooptically controlling the relative phase between the 1064-nm fundamental and the 532-nm second-harmonic fields in a dispersion crystal section between two periodically poled lithium niobate (PPLN) sections. Theoretical derivation and experimental demonstration were carried out for two novel crystal configurations, including a linear cascaded configuration in which a 1-cm dispersion section is sandwiched between two 2-cm PPLN sections, and a folding-crystal high-efficiency configuration in which the mixing waves traverse twice in a 2-cm PPLN section through total internal reflections in a 1.5-cm dispersion section. Due to the coherence enhancement in the constructive phase between the two second-harmonic generation (SHG) fields in the two PPLN sections, we measured a 30% increase in conversion efficiency compared to a 4-cm continuous-grating PPLN under the same condition. The measured half-wave voltage for the amplitude modulation is 1.1 V × d (μm)/ld (cm), where d is the separation of the electrodes and ld is the length of the electrodes. View full abstract»

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  • Analysis of deep waveguide gratings: an efficient cascading and doubling algorithm in the method of lines framework

    Page(s): 1204 - 1209
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (286 KB) |  | HTML iconHTML  

    In this work, a computationally fast, numerically stable, and memory-efficient cascading and doubling algorithm is proposed within the method of lines framework to model long planar waveguide gratings having thousands of periods in the propagation direction. This algorithm can model 2n grating periods in n calculational steps and needs N2 matrices for N sample points in the problem space. It can model periodic, quasi-periodic, symmetric, and asymmetric gratings efficiently. Different deep waveguide gratings are modeled using this scheme and results for the fundamental TE mode spectral reflectivity are compared with published results showing excellent agreement. View full abstract»

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  • High-accuracy finite-difference equations for dielectric waveguide analysis I: uniform regions and dielectric interfaces

    Page(s): 1210 - 1218
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (395 KB)  

    A methodology is presented that allows the derivation of low-truncation-error finite-difference representations or the two-dimensional Helmholtz equation, specific to waveguide analysis. This methodology is derived from the formal infinite series solution involving Bessel functions and sines and cosines. The resulting finite-difference equations are valid everywhere except at dielectric corners, and are highly accurate (from fourth to sixth order, depending on the type of grid employed). None the less, they utilize only a nine-point stencil, and thus lead to only minor increases in numerical effort compared with the standard Crank-Nicolson equations. View full abstract»

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  • Mode coupling contribution to radiation losses in curvatures for high and low numerical aperture plastic optical fibers

    Page(s): 1160 - 1164
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (227 KB) |  | HTML iconHTML  

    We have studied the optical power losses due to multiple curvatures in polymethylmetacrylate (PMMA) plastic optical fibers (POFs) of different numerical apertures (NAs) and attenuation. The fibers were tested for several configurations in order to assess the influence of different types of curved-to-straight fiber transitions in the amount of power radiation. We found that losses are below the standards for all tested fiber types, and thus, they are a suitable choice for local area network (LAN) applications. In addition, our results revealed the presence of modal interactions as confirmed using an experimental procedure to estimate the mode coupling strength for the same fibers. View full abstract»

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  • A deterministically controlled four-segment polarization-mode dispersion emulator

    Page(s): 1132 - 1140
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (311 KB) |  | HTML iconHTML  

    In this paper, we propose a novel design of a first- and second-order polarization-mode dispersion (PMD) emulator based on four concatenated first-order PMD segments. Instead of polarization scrambling at each junction, we set these polarization rotators according to a statistical schedule, so as to produce a realistic probability density function of the first- and second-order PMD presented in long-haul transmission fiber. View full abstract»

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  • Measure of twist-induced circular birefringence in long single-mode fibers: theory and experiments

    Page(s): 1149 - 1159
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (376 KB) |  | HTML iconHTML  

    Production defects and external perturbations cause standard telecommunication fibers to be randomly birefringent. Fiber birefringence is the origin of the well-known polarization mode dispersion (PMD), which degrades system performances. The knowledge of birefringence properties may be crucial, especially when problems like development of low-PMD fibers or PMD interaction with optical nonlinearities in very high-capacity systems are faced. Some techniques are known to measure birefringence, and useful results have been obtained for both installed and wound-on-drum fibers. However, measurement of the circular component of birefringence still presents difficulties. In this paper, a new method for circular birefringence measurement is proposed that applies to long single-mode twisted fibers. The technique is based on polarization-sensitive optical time-domain reflectometry. Experimental results are in good agreement with the theoretical analysis. View full abstract»

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  • Experimental and theoretical characterization of a 40-Gb/s long-haul single-channel transmission system

    Page(s): 1124 - 1131
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (363 KB) |  | HTML iconHTML  

    We present a comparison between experiment and simulation of a 40-Gb/s periodically stationary dispersion-managed soliton (DMS) system in a recirculating loop. We find that we can propagate an error-free signal over 6400 km at 40 Gb/s and over 12 000 km if we lower the data rate to 10 Gb/s, keeping all other parameters constant. A careful analysis of the limiting factors shows the strong influence of nonlinear optical pulse-to-pulse interactions, causing a large increase in timing jitter. At a transmission distance of 6400 km, a large fraction of the jitter is due to pulse-to-pulse interactions. Moreover, we find that the system performance is very sensitive to parameter variations. We conclude that periodically stationary DMS systems suffer from numerous problems when increasing the data rate, suggesting that it may be impractical for wavelength-division multiplex transmission at 40 Gb/s. View full abstract»

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  • Topology and shape optimizations of substrates for chirp fiber Bragg grating spectrum tuning

    Page(s): 1182 - 1187
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (396 KB)  

    A systematic method based on topology and shape optimization techniques has been developed to determine the geometry of a substrate for chirp fiber Bragg grating (FBG) spectrum tuning. The strain distribution on the FBG associated with a given wavelength spectrum is synthesized first by the application of a genetic algorithm. Then the substrate profiles determined either from topology or shape optimizations can generate the required strain distribution on FBG that responds to the required wavelength spectrum of a chirp FBG. The profile obtained from shape optimization, compared with that from topology optimization, has clear advantages in easier manufacturing and better liability. Although the strain distribution of a chirp FBG demonstrated here is simple in this study, it should be emphasized that this methodology also can be easily applied to determine other substrate profile whose strain distribution is regarding to a more complex wavelength spectrum of an FBG. View full abstract»

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  • The RP method: a new tool for the iterative solution of the nonlinear Schrodinger equation

    Page(s): 1102 - 1112
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (422 KB) |  | HTML iconHTML  

    An original approach to the solution of the nonlinear Schrodinger equation (NLSE) is pursued in this paper, following the regular perturbation (RP) method. Such an iterative method provides a closed-form approximation of the received field and is thus appealing for devising nonlinear equalization/compensation techniques for optical transmission systems operating in the nonlinear regime. It is shown that, when the nonlinearity is due to the Kerr effect alone, the order n RP solution coincides with the order 2n + 1 Volterra series solution proposed by Brandt-Pearce and co-workers. The RP method thus provides a computationally efficient way of evaluating the Volterra kernels, with a complexity comparable to that of the split-step Fourier method (SSFM). Numerical results on 10 Gb/s single-channel terrestrial transmission systems employing common dispersion maps show that the simplest third-order Volterra series solution is applicable only in the weakly nonlinear propagation regime, for peak transmitted power well below 5 dBm. However, the insight in the nonlinear propagation phenomenon provided by the RP method suggests an enhanced regular perturbation (ERP) method, which allows the first order ERP solution to be fairly accurate for terrestrial dispersion mapped systems up to launched peak powers of 10 dBm. View full abstract»

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  • High-accuracy finite-difference equations for dielectric waveguide analysis II: dielectric corners

    Page(s): 1219 - 1231
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (504 KB)  

    For part I see ibid., p. 1210, 2002. We present a discussion of the behavior of the electric and magnetic fields satisfying the two-dimensional Helmholtz equation for waveguides in the vicinity of a dielectric corner. Although certain components of the electric field have long been known to be infinite at the corner, it is shown that all components of the magnetic field are finite, and that finite-difference equations may be derived for these fields that satisfy correct boundary conditions at the corner. These finite-difference equations have been combined with those derived in the previous paper to form a full-vector waveguide solution algorithm of unprecedented accuracy. This algorithm is employed to provide highly accurate solutions for the fundamental modes of a previously studied standard rib waveguide structure. View full abstract»

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  • Theoretical interpretation of the enhanced single-mode stability in extended cavity VCSELs

    Page(s): 1173 - 1181
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (427 KB) |  | HTML iconHTML  

    Paraxial eigenmode analysis demonstrates that the extended cavity stability follows from the geometric scaling of the diffractive cavity losses; the same principle also explains the narrow aperture stability. Because diffraction losses scale as (L/b)2 = (Lλ/πwo2)2, one can enhance diffraction to differentiate thresholds among modes either by shrinking the mode waist wo (smaller aperture) or by extending the cavity length L. The second approach does not limit the vertical cavity semiconductor laser (VCSEL) output power. Our predictions agree with experimental trends, and suggest that diffraction limited modes apply to extended cavity VCSELs, since guided mode theory (effective index or thermal lensing) does not allow strong stability dependence on cavity length. The extended length stabilization holds when factors other than diffraction (such as mode wing clipping or aperture scattering) significantly contribute to cavity losses. View full abstract»

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  • Analytical calculation of pulse broadening in optical higher order PMD compensation

    Page(s): 1118 - 1123
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (275 KB) |  | HTML iconHTML  

    The system performances in second- and third-order polarization mode dispersion (PMD) compensations have been calculated analytically and a proper approach for the higher order PMD compensation has been investigated. The investigation has revealed that the frequency averaged higher order terms of the fiber link's PMD vector should be used as the coefficient vectors in emulating the frequency dependent compensation vector for higher order PMD compensation. View full abstract»

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  • Pulse restoration by filtering of self-phase modulation broadened optical spectrum

    Page(s): 1113 - 1117
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (307 KB) |  | HTML iconHTML  

    Restoration of distorted optical pulses is achieved using nonlinear fiber self-phase spectral broadening and subsequent optical band-pass filtering of a single sideband. Using this technique, the output pulsewidth is shown to remain constant for input pulse-widths between 9-20 ps. A detailed investigation of the signal-to-noise ratio shows that best performance is obtained by operating in normal fiber dispersion regime. This technique is also applied to restore 40 Gb/s RZ-data suffering distortion from polarization mode dispersion. The high-bandwidth fiber nonlinearity shows promise to scale to higher bit rate pulse distortion correction. View full abstract»

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  • Scaling laws for MEMS mirror-rotation optical cross connect switches

    Page(s): 1084 - 1094
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (402 KB) |  | HTML iconHTML  

    The design of large-scale mirror-rotation free-space optical cross-connect switches based on arrays of microelectromechanical torsion mirrors is considered. The layout of a compact switch is first presented. The parameters of the Gaussian beam that maximizes the port count for a given mirror turn angle is then identified, and the supporting optical system needed to create the desired beam is defined. Scaling laws for the optical path length needed for a given number of ports are then derived. Numerical simulations are used to verify the ideal configuration, and scaling laws are proposed for various departures from the ideal. It is shown that ideal operation can still be maintained when the mirrors are curved, and operating conditions that minimize the effect of mirror curvature are identified. View full abstract»

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  • Design of a 10-Gb/s burst-mode optical packet receiver module and its demonstration in a WDM optical switching network

    Page(s): 1078 - 1083
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (270 KB) |  | HTML iconHTML  

    A 10-Gb/s burst-mode optical packet receiver module was fabricated. Its sensitivity was -24.8 dBm. Its sensitivity penalty due to packet-arrival timing jitter was less than 1.5 dB in arbitrary relative phase, and its total sensitivity penalty due to power fluctuation and packet-arrival timing jitter was less than 2.9 dB when the magnitude of packet-by-packet power fluctuation was 9 dB. We experimentally confirmed that our burst-mode optical packet receiver did not cause a penalty for wavelength division multiplexed (WDM) optical switching using the wavelength channel selector module. 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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Meet Our Editors

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