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Lightwave Technology, Journal of

Issue 11 • Date Nov. 2005

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Displaying Results 1 - 25 of 67
  • [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): 3421 - 3422
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  • Guest Editorial Special Issue on Optical Fibers

    Page(s): 3423 - 3425
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    Freely Available from IEEE
  • Dispersion-tailored few-mode fibers: a versatile platform for in-fiber photonic devices

    Page(s): 3426 - 3443
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (736 KB) |  | HTML iconHTML  

    In-fiber devices enable a vast array of critical photonic functions ranging from signal conditioning (amplification, dispersion control) to network management (add/drop multiplexers, optical monitoring). These devices have become mainstays of fiber-optic communication systems because they provide the advantages of low loss, polarization insensitivity, high reliability, and compatibility with the transmission line. The majority of fiber devices reported to date are obtained by doping, designing, or writing gratings in the core of a single-mode fiber (SMF). Thus, these devices use the fiber only as a platform for propagating light-the device effect itself is due to some extraneously introduced material or structure (dopants for amplification, gratings for phase matching, etc.) There exists another, relatively less explored degree of freedom afforded by fibers-the ability to copropagate more than one mode. Each mode may have a uniquely defined modal dispersion and propagation characteristic. In this paper, we will describe the variety of fiber devices enabled by few-mode fibers-fibers that typically support two to four modes with suitably tailored dispersive properties. We will show that the unique dispersive properties of various modes, in conjunction with the ability to couple between them with gratings, leads to devices that offer novel solutions for dispersion compensation, spectral shaping, and polarization control, to name a few. View full abstract»

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  • Segmented-clad fiber design for tunable leakage loss

    Page(s): 3444 - 3453
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    This paper proposes a novel segmented-clad fiber (SCF) design in which the spectral variation of leakage loss of the fundamental mode can be finely tuned by varying the fiber parameters. A fiber with such optimized spectral variation of leakage loss should find application in the realization of inherently gain-flattened optical fiber amplifiers, wavelength filters, wavelength-flattened attenuators, etc. In this paper, the authors present SCF designs optimized for realizing inherently gain-flattened S-band erbium-doped fiber amplifier (EDFA) and high-gain discrete Raman fiber amplifier (RFA). Amplifier characteristics have been modeled in both cases, and simulations show that a 20-dB gain with ±0.9 dB of gain ripple over a 30-nm bandwidth in S-band is achievable with the designed EDFA based on the optimized SCF. In case of discrete RFA based on SCF, a 20-dB net gain with ±0.5-dB ripple is shown to be achievable over a 28-nm wavelength range in S-band. View full abstract»

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  • High bandwidth single polarization fiber with elliptical central air hole

    Page(s): 3454 - 3460
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    A novel design of single polarization fiber is presented. The structure of the fiber comprises an elliptical central air hole with depressed cladding surrounding the core. Parameters that affect the performance of the single polarization fiber in terms of the location of the single polarization operating window and single polarization bandwidth are analyzed. The analysis results in the identification of a fiber design that can yield a single polarization bandwidth as high as 240 nm around 1550 nm. View full abstract»

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  • Measuring thermal and mechanical stresses on optical fiber in a DC module using fiber Bragg gratings

    Page(s): 3461 - 3468
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (264 KB) |  | HTML iconHTML  

    Fiber Bragg gratings (FBGs) can be used as sensors to monitor stress and test temperature during the processing and handling of optical fiber. As the FBG experiences a combination of mechanical and thermal loading, the return Bragg wavelength will shift proportionately to the magnitude of the load. This paper discusses the use of these sensors in quantifying induced stress on fiber during the packaging of a dispersion-compensating module (DCM) and the ensuing environmental exposure. There are two potential fiber-failure modes for fiber wound in DCMs, namely microbend-induced attenuation and fiber failure from fatigue. The ability to quantify fiber stress provides a useful feedback tool in the design phase of these modules that can aid in reducing the risk of mechanical and optical failure modes. A practical characterization process was developed to decouple thermal and stress effects on FBGs based on results from current literature and from this study. Uncoated Bragg sensors were found to respond linearly between -40 to 80°C. Gratings with a protective polymer recoat departed from the linear behavior of the uncoated gratings below -5°C. It was determined that the recoat material places less than 25 MPa (3.6 klbf/in2) of axial compression on the fiber at -40°C. Four gratings with different Bragg wavelengths were spliced into 10 km of fiber and wound into a DCM. The wind-induced stress on all four gratings quickly relaxed. The module was then thermal cycled between -40 and +75°C. The overall stress on each grating was acceptably low for reliability purposes. The maximum stress of 17 MPa (2.5 klbf/in2) was observed at the lowest temperature. View full abstract»

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  • Dispersion-compensation module based on one preform design matching arbitrary dispersion and slope requirements

    Page(s): 3469 - 3474
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    In this article, we propose a method to realize dispersion-compensation modules (DCMs) with a user-defined dispersion in a specified bandwidth for a given tolerance. It is based on the wavelength shift of a characteristic dispersion function by scaling the refractive-index profile. Controlling the fiber diameter during the manufacturing process leads to the desired scaling. In order to get a DCM with the predefined wavelength-dependent dispersion, a specific diameter-versus-position function has to be implemented. To demonstrate the concept, compensators for typical transmission fibers were simulated. For example, the dispersion in the complete C band (1530-1570 nm) can be compensated for 100 km of TeraLight and TrueWave-RS. The results showed a residual dispersion of only ±1 ps/nm and could be realized with overall compensator lengths of 3.54 and 1.97 km, respectively. Furthermore, higher order dispersion in the S, C, and L bands (1490-1610 nm) was compensated for different requirements with a tolerance of only ±0.5 ps/nm, which enables ultrahigh bit-rate transmission at 160 Gb/s. In order to estimate the feasibility of such a DCM, a tolerance analysis is presented, and the guiding properties are approximated. View full abstract»

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  • Highly nonlinear fiber-based lumped fiber Raman amplifier for CWDM transmission systems

    Page(s): 3475 - 3483
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    The highly nonlinear fiber (HNLF)-based lumped fiber Raman amplifiers (LRAs) for four- and eight-channel coarse wavelength division multiplexing (CWDM) transmission systems have been investigated. By using the developed LRA, the four-channel CWDM transmission over conventional single-mode fiber (SMF) with the length of 150 km has been successfully achieved. View full abstract»

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  • A detailed experimental study on single-pump Raman/EDFA hybrid amplifiers: static, dynamic, and system performance comparison

    Page(s): 3484 - 3493
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    This paper presents an experimental study on the performance comparison of three different schemes of single-pump dispersion-compensating fiber (DCF)-based Raman/erbium-doped fiber amplifier (EDFA) hybrid amplifiers together with a DCF-based Raman-only amplifier in terms of static properties, dynamic properties, and system impact: Raman-only amplifier (Type I), Raman/EDFA hybrid amplifiers recycling residual Raman pump in a cascaded EDF located either after (Type II) or prior to (Type III) a DCF, and a Raman-assisted EDFA (Type IV), the concept of which was proposed by Kurosawa et al. With respect to the overall gain and system impact based on bit error rate (BER) measurements in a transmission system, the hybrid amplifier of Type II was found to have the best performance among the four types while the Raman-only amplifier shows the best tolerance to transient response. View full abstract»

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  • Low-bending-loss single-mode fibers for fiber-to-the-home

    Page(s): 3494 - 3499
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    Recent progress on low-bending-loss single-mode optical fibers for fiber-to-the-home (FTTH) is reviewed. Designing and manufacturing for three types of fibers-a step-index-profile fiber, a trench-index-profile fiber, and a holey fiber-are discussed. The trench-index-profile fibers and the holey fibers are confirmed to be candidates for indoor wiring because of their low bending losses, as well as splice losses. View full abstract»

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  • Germania-based core optical fibers

    Page(s): 3500 - 3508
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    Germania-glass-based core silica glass cladding single-mode fibers (Δn up to 0.143) with a minimum loss of 20 dB/km at 1.9 μm were fabricated by the modified chemical vapor deposition (MCVD) method. The fibers exhibit strong photorefractivity with the type-IIa-induced refractive-index modulation of 2×10-3. The Raman gain of 300 to 59 dB/(km·W) was determined at 1.07 to 1.6 μm, respectively, in a 75 mol.% GeO2 core fiber. Only 3 m of such fibers are enough for the creation of a 10-W Raman laser at 1.12 μm with a 13-W pump at 1.07 μm. Raman generation in optical fiber at a wavelength of 2.2 μm was obtained for the first time. View full abstract»

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  • Modeling of stimulated Brillouin scattering in optical fibers with arbitrary radial index profile

    Page(s): 3509 - 3516
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    Stimulated Brillouin scattering (SBS) is an impairment seen in narrowband transmission over optical telecommunications fiber at high laser power. Accurate modeling is necessary to predict the strength of this phenomenon. One method of SBS control is the optimal design of the fiber radial index of refraction profile. Previous work has been limited to modeling optical fibers with one or more radial step changes in index. Here, the author derives and solves a general set of differential equations that allow the numerical solution of SBS spectral gain for an arbitrary radial index profile. Simulated and measured spectra are compared for several fibers with GeO2-doped cores. It is found that radial material displacement plays a significant role in the SBS interaction in fibers with a complex radial index profile. View full abstract»

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  • Heating of hollow photonic Bragg fibers from field propagation, coupling, and bending

    Page(s): 3517 - 3525
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    We investigate heating from field propagation, coupling, and bending, which are the potential failure mechanisms for an emerging new type of high-power radiation guides-hollow photonic Bragg fibers. Continuous wave (CW) and pulsed radiation sources are considered, assuming continuous operation of the laser source. View full abstract»

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  • Opportunities to enhance multimode fiber links by application of overfilled launch

    Page(s): 3526 - 3540
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    This paper investigates possibilities for the practical design of high-performance multimode fibers (MMFs) that can provide bandwidths in excess of 10 GHz·km in an overfilled regime of operation. Analysis of standard MMF in an overfilled launch demonstrates that the theoretical bandwidth limitations arise from the influence of cladding on the propagation of the highest order modes. Practical MMF profile designs that overcome this problem are investigated. The standard 50- and 62.5-μm fiber profiles are redesigned first to allow for the performance in an overfilled launch with the differential mode delays (DMDs) below 0.055 and 0.250 ns/km, respectively. It is shown that such fibers can exhibit the same or better theoretical bandwidth in an overfilled launch when compared to standard fiber under restricted launch. Elimination of the need for the restricted mode launch in high-performance multimode transmission systems can improve reliability issues and can relax the range of tolerance requirements imposed on terminal equipment, optical components, and link installation. Furthermore, MMFs that can be operated in an overfilled launched are compatible with emerging vertical cavity surface emitting laser (VCSEL) wavelength division multiplexing (WDM) array technologies. A successfully controlled higher order mode DMD also allows for the reduction of MMF core size and Δ that can be beneficial for low-cost high-performance single-channel links. It is demonstrated that properly designed reduced core fibers can achieve theoretical DMDs in the range of 0.005-0.02 ns/km. The bend loss properties of redesigned fibers are investigated in detail, showing that the proposed modifications do not lead to significant degradation of bend loss performance. Moreover, they can be manufactured at considerably lower cost while utilizing commercially readily available low-cost VCSELs. Even where the theoretical limit is not achieved by practical fiber making, the reduced core size and Δ MMF can provide higher production yield, lower cost, and higher average bandwidth. View full abstract»

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  • Low-loss pure-silica-core fibers and their possible impact on transmission systems

    Page(s): 3541 - 3550
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    Low-loss optical fibers are now indispensable transmission media for transmission systems. Recently, the ultralow-loss performance for long transmission systems, the water-loss-free performance for wide-band wavelength-division-multiplexing (WDM) systems, the hydrogen-loss-insensitive performance for system reliability, and the bending-loss-insensitive performance for access or indoor applications have attracted much interest. In this regard, pure-silica-core fibers (PSCFs) are suitable, and unprecedented low-loss PSCFs have been successfully fabricated. This paper introduces the recent progress of low-loss PSCFs and their possible impact on transmission systems. View full abstract»

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  • Binary multi-zoned microstructured fiber: a comparative dispersion analysis of radially chirped Bragg fiber

    Page(s): 3551 - 3557
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    We analyze binary radially chirped Bragg fiber (RCBF) having the geometry of a binary multi-zoned microstructured fiber (MSF). As it is, in effect, a longitudinally extended binary Fresnel lens, we find that it propagates light via periodic refocusing into the center of the fiber. Zoning produces unusual dispersion properties, so we present a comparative analysis with other zoned MSF geometries, such as single-mode fiber (SMF; effectively consisting of only one zone) and conventional (unchirped) Bragg fiber. We perform an eigenmode expansion of Maxwell's equations for the three fiber geometries and find that the SMF and Bragg fiber have similar modal dispersion, with monotonic waveguide dispersion for all modes at high frequencies, whereas RCBF exhibits oscillatory behavior, with modal dispersion varying between positive and negative values as the frequency increases. This demonstrates that zoning introduces flexibility in the engineering of desired waveguide-dispersion characteristics. View full abstract»

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  • PCF-based polarization splitters with simplified structures

    Page(s): 3558 - 3565
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    We propose novel polarization splitters based on photonic crystal fibers (PCFs), in which the cores of the splitters are nearly nonbirefringent. Different from conventional fiber-based polarization splitters, the birefringence in the new splitters results mainly from narrow silica regions physically connecting the two cores. This means that polarization splitting can be achieved without employing highly birefringent cores, which provides a possibility to greatly simplify the structures of the PCF-based polarization splitters and make them more practical. A 5-mm-long splitter with an extinction ratio of 20 dB has been obtained. We also discuss how the silica regions influence coupling characteristics of the dual-core PCFs and present a design guidance for the polarization splitters based on polarization-dependent coupling. View full abstract»

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  • Dispersion-compensating fibers

    Page(s): 3566 - 3579
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    This paper reviews properties and use of conventional single-mode dispersion-compensating fibers (DCFs). The quality of the dispersion compensation expressed as residual dispersion after compensation is treated. Properties of actual DCFs for discrete compensation including loss and nonlinear effects are discussed. Fiber design with special emphasis on design tradeoffs is considered. The Raman properties of DCFs and their use as a discrete Raman amplifier are also discussed. Finally, DCF for use in dispersion-managed cables (DMCs) is addressed, including optimum fiber design and comparison of different configurations. View full abstract»

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  • Numerical modeling of photonic crystal fibers

    Page(s): 3580 - 3590
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    Recent progress on numerical modeling methods for photonic crystal fibers (PCFs) such as the effective index approach, basis-function expansion approach, and numerical approach is described. An index-guiding PCF with an array of air holes surrounding the silica core region has special characteristics compared with conventional single-mode fibers (SMFs). Using a full modal vector model, the fundamental characteristics of PCFs such as cutoff wavelength, confinement loss, modal birefringence, and chromatic dispersion are numerically investigated. View full abstract»

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  • Highly nonlinear bismuth-oxide fiber for supercontinuum generation and femtosecond pulse compression

    Page(s): 3591 - 3596
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    Highly nonlinear normally dispersive bismuth-oxide fiber shows promise for applications such as supercontinuum generation and femtosecond pulse compression in the telecommunications-wavelength range. To generate a wideband and flat supercontinuum spectrum, the balance between fiber nonlinearity and normal group velocity dispersion (GVD) is important. Highly nonlinear bismuth-oxide fiber exhibits a large nonlinearity due to the small effective area and nonlinear index of the host glass material. The fiber also has a relatively flat dispersion profile over a large wavelength range. Utilizing these features, we generate a smooth unstructured supercontinuum between 1200 and 1800 nm. This supercontinuum is passed through a grating pair, and pulses, originally of 150-fs length, are compressed to 25 fs. View full abstract»

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  • Analyzing the fundamental properties of Raman amplification in optical fibers

    Page(s): 3597 - 3605
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    The Raman response of germanosilicate fibers is presented. This includes not only the material dependence but also the relation between the spatial-mode profile of the light and the Raman response in the time and frequency domain. From the Raman-gain spectrum, information is derived related to the nonlinear refractive index due to nuclear motions and the Raman response function in the time domain. It is demonstrated that the Raman-gain coefficient may be reduced up to 60% if the signal propagates in the fundamental mode while the pump alternates between the fundamental mode and a higher order mode. A simple model shows that the time response related to the decay of phonons is significantly larger in germanate glass relative to silica glass. From the Raman gain, it is found that the contribution to the nonlinear refractive index from nuclear motions is reduced by a factor of 2 in germanate relative to silica glass. View full abstract»

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  • Nonlinear fibers for signal processing using optical Kerr effects

    Page(s): 3606 - 3614
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    This paper reviews nonlinear optical-fiber designs for signal processing using optical Kerr effects. The requirements for designing nonlinear fibers are described first. Then, the design concept is discussed and design examples are shown to illustrate the tradeoffs among the different fiber properties such as effective area, dispersion, and attenuation. Furthermore, fiber designs with distributed Brillouin frequency shift to mitigate the effect of simulated Brillouin scattering (SBS) in nonlinear fibers are discussed in detail. An SBS-threshold increase of 7 dB over conventional nonlinear fibers is experimentally demonstrated. View full abstract»

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  • Low-loss and low-dispersion-slope highly nonlinear fibers

    Page(s): 3615 - 3624
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    In recent technologies, various optical signal processing systems have been reported. In many of these applications, highly nonlinear fibers (HNLFs) are used as key parts. Especially, low loss and low dispersion slope are critical features of the HNLFs. In this paper, their design and characteristics, packaging technology, and applications are introduced. 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