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Lightwave Technology, Journal of

Issue 9 • Date Sept. 2005

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Displaying Results 1 - 25 of 32
  • [Front cover]

    Page(s): c1
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  • Journal of Lightwave Technology publication information

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  • Table of contents

    Page(s): 2597
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  • Routing, wavelength and time-slot-assignment algorithms for wavelength-routed optical WDM/TDM networks

    Page(s): 2598 - 2609
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    This paper studies the connection-assignment problem for a time-division-multiplexed (TDM) wavelength-routed (WR) optical wavelength-division-multiplexing (WDM) network. In a conventional WR network, an entire wavelength is assigned to a given connection (or session). This can lead to lower channel utilization when individual sessions do not need the entire channel bandwidth. This paper considers a TDM-based approach to reduce this inefficiency, where multiple connections are multiplexed onto each wavelength channel. The resultant network is a TDM-based WR network (TWRN), where the wavelength bandwidth is partitioned into fixed-length time slots organized as a fixed-length frame. Provisioning a connection in such a network involves determining a time-slot assignment, in addition to the route and wavelength. This problem is defined as the routing, wavelength, and time-slot-assignment (RWTA) problem. In this paper, we present a family of RWTA algorithms and study the resulting blocking performance. For routing, we use the existing shortest path routing algorithm with a new link cost function called least resistance weight (LRW) function, which incorporates wavelength-utilization information. For wavelength assignment, we employ the existing least loaded (LL) wavelength selection; and for time-slot allocation, we present the LL time-slot (LLT) algorithm with different variations. Simulation-based analyses are used to compare the proposed TDM architecture to traditional WR networks, both with and without wavelength conversion. The objective is to compare the benefits of TDM and wavelength conversion, relative to WR networks, towards improving performance. The results show that the use of TDM provides substantial gains, especially for multifiber networks. View full abstract»

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  • A robust fiber-radio architecture for wavelength-division-multiplexing ring-access networks

    Page(s): 2610 - 2620
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    In this paper, we propose a dynamic wavelength-allocation scheme for wavelength-division multiplexing (WDM) fiber-radio ring-access networks. This scheme can be used to improve the use efficiency of wavelengths at the burst traffic load on the fiber-radio networks. Moreover, a novel bidirectional wavelength add-drop multiplexer (B-WADM) is designed on the backboned ring, which can connect the working and standby sub-rings. It can provide the self-protected function that uses just a few optical devices under link failures. Furthermore, we carry out this study through the simulation and analysis for carrier-to-noise ratio (CNR), channel capacity, and spurious free dynamic range (SFDR) of the fiber-radio network. Finally, we set up an experimental network to demonstrate its performance. The experimental results illustrate that this fiber-radio architecture can provide the robust, flexible, and reliable characteristics for large radio terminals. View full abstract»

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  • WDM access system based on shared demultiplexer and MMF links

    Page(s): 2621 - 2628
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    A wavelength-division-multiplexing (WDM) access system can be used in two basic ways: user multiplexing, which assigns a wavelength to each user, and service multiplexing, which assigns a wavelength to each service. In current designs for service multiplexing, each optical network unit (ONU) must have a demultiplexer that can select any wavelength. This paper proposes a new WDM access system that uses one demultiplexer shared by many ONUs to offer optical-distribution access services. This system realizes significant cost reductions due to its passive optical network (PON) architecture, high capacity due to its WDM technology, and easy wiring through the use of multimode fiber (MMF). As one of the realization approaches of the shared demultiplexer, we explain the principle and configuration of a shared demultiplexer based on diffraction theory, and present theoretical and experimental analyses of a prototype 4×(4×4) shared demultiplexer whose configuration is based on Littrow mounting. Experimental transmission performances demonstrate the feasibility of the proposed WDM access system. View full abstract»

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  • Smooth upgrade of existing passive optical networks with spectral-shaping line-coding service overlay

    Page(s): 2629 - 2637
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    A simple and cost-effective upgrade of existing passive optical networks (PONs) is proposed, which realizes service overlay by novel spectral-shaping line codes. A hierarchical coding procedure allows processing simplicity and achieves desired long-term spectral properties. Different code rates are supported, and the spectral shape can be properly tailored to adapt to different systems. The computation can be simplified by quantization of trigonometric functions. DC balance is achieved by passing the dc residual between processing windows. The proposed line codes tend to introduce bit transitions to avoid long consecutive identical bits and facilitate receiver clock recovery. Experiments demonstrate and compare several different optimized line codes. For a specific tolerable interference level, the optimal line code can easily be determined, which maximizes the data throughput. The service overlay using the line-coding technique leaves existing services and field-deployed fibers untouched but fully functional, providing a very flexible and economic way to upgrade existing PONs. View full abstract»

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  • Theoretical investigation of optical wavelength conversion techniques for DPSK Modulation formats using FWM in SOAs and frequency comb in 10 gb/s transmission systems

    Page(s): 2638 - 2646
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    We have investigated the wavelength conversion techniques for differential phase-shift keying (DPSK) modulation formats in 10 Gb/s transmission systems, compared with the non-return-to-zero (NRZ) modulation format. For the wavelength conversion of DPSK modulation formats, we employed the wavelength converters based on the four-wave mixing (FWM) in semiconductor optical amplifiers (SOAs) and the frequency comb generated by phase modulation. The power penalty at 10-9 bit error rate was used as a measure of the system performance degraded by the wavelength conversion. Our simulation results show that the DPSK modulation formats have a smaller power penalty than the NRZ modulation format for the wavelength conversion using the FWM effect in an SOA due to a much lower pattern effect. However, as the wavelength conversion uses the frequency comb generated by phase modulation, it has a similar power penalty compared with the NRZ modulation format. It is also shown that the DPSK modulation formats are possible to obtain the power penalty less than 0.4 dB for both wavelength conversion techniques. View full abstract»

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  • Transmission improvement in ultralong dispersion-managed soliton WDM systems by using pulses with different widths

    Page(s): 2647 - 2653
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    It was shown that one can improve transmission performance in ultra-long-haul wavelength-division-multiplexed (WDM) systems by matching the input pulsewidth to the path-averaged dispersion (PAD) in the line. Wider pulses should be used for higher values of PAD, and vice versa. It was also noted that this pulsewidth selection is only effective in the dispersion-managed soliton (DMS) propagation regime but not in the chirped return-to-zero (CRZ) regime. View full abstract»

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  • OTDM add-drop multiplexer based on XPM-induced wavelength shifting in highly nonlinear fiber

    Page(s): 2654 - 2661
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    In this paper, we study experimentally and numerically simultaneous time-domain add-drop multiplexing for high-speed optical time-division multiplexing (OTDM) networks based on cross-phase-modulation (XPM)-induced wavelength shifting in a 50-m highly nonlinear fiber. This scheme needs only a single-channel clock rate and does not alter the input signal wavelength. Simultaneous add and drop operations at 80 Gb/s have been demonstrated experimentally with less than 1-dB power penalty for the dropped channel and no distinct bit-error-rate (BER) degradation for the added channel. Numerical simulations show that the experimental results are only limited by the available signal pulsewidth, and simultaneous add-drop multiplexing at 160-Gb/s or higher bit rates is possible with this scheme by employing control and signal pulses with proper pulsewidths. View full abstract»

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  • Analysis of the effect of thermal chirp on interferometric homodyne and heterodyne crosstalk in optical communication systems employing directly Modulated DFB lasers

    Page(s): 2662 - 2672
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    A closed-form expression is derived for the probability density function (pdf) of the beat noise created by homodyne and heterodyne interferometric crosstalk in optical communication systems employing directly modulated distributed feedback lasers at bit rates between 155 Mb/s and 2.5 Gb/s. Thermal chirp is shown to be the predominant chirp mechanism affecting homodyne-crosstalk-induced penalty at bit rates up to 2.5 Gb/s. Theoretical calculations of the crosstalk-induced power penalty are verified experimentally. View full abstract»

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  • BER performance due to irregularity of row-weight distribution of the parity-check matrix in irregular LDPC codes for 10-gb/s optical signals

    Page(s): 2673 - 2680
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    Forward-error correction (FEC) coding is theoretically investigated to improve bit-error-rate (BER) performance in a 10-Gb/s optical transmission system using randomly irregular low-density parity-check (LDPC) codes, regular LDPC codes, and the Reed-Solomon (RS) (255,239) code as a comparison. The irregular LDPC codes has different row-weight variances of a parity-check matrix from 10.9 to 18.8 and a row-weight mean of 60. Simulation is carried out under various conditions including the impairment factors such as dispersion, polarization-mode dispersion (PMD), and fiber nonlinearities. Results suggest that the irregular LDPC code with a low row-weight variance (=10.9) generally has better performance for the most impairment factors except for the factor of dispersion. On the other hand, for the factor of dispersion the irregular LDPC code performs better with a high row-weight variance (=18.8). A specific LDPC code can overcome the impairment limits in a deployed link. View full abstract»

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  • Analysis of direct-detection DPSK signal with homodyne crosstalk

    Page(s): 2681 - 2686
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    When a differential-phase-shift-keying (DPSK) signal is directly detected using an asymmetric interferometer and balanced receiver, the exact error probability of the signal with homodyne crosstalk is derived analytically. Homodyne crosstalk from many interferers is Gaussian distributed, but the Gaussian model overestimates the signal-to-noise ratio (SNR) penalty for homodyne crosstalk from a single interferer. For the DPSK signal, the crosstalk ratio for a 1-dB SNR penalty must be less than -16.5 dB. For the same crosstalk ratio, the SNR penalty for a DPSK signal is far smaller than that for an ON-OFF keying (OOK) signal. View full abstract»

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  • Optical generation and distribution of continuously tunable millimeter-wave signals using an optical phase modulator

    Page(s): 2687 - 2695
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    In this paper, we propose an approach to generate and distribute two wide bands of continuously tunable millimeter-wave (mm-wave) signals using an optical phase modulator and a fixed optical notch filter. We demonstrate theoretically that the odd-order electrical harmonics are cancelled and even-order electrical harmonics are generated at the output of a photodetector when the optical carrier is filtered out from the phase-modulated optical spectrum. Analysis shows that dispersion compensation is required in order to maintain the suppression of the odd-order electrical harmonics, in order to eliminate signal fading of the generated electrical signal when the optical signal is distributed using conventional single-mode optical fiber. It is experimentally demonstrated that, when the electrical drive signal is tuned from 18.8-25 GHz, two bands of mm-wave signals from 37.6 to 50 GHz and from 75.2 to 100 GHz with high signal quality are generated locally and remotely. This approach does not suffer from the direct current (dc) bias-drifting problem observed when an optical intensity modulator is used. View full abstract»

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  • Performance improvement of phase-shift-keying signal transmission by means of optical limiters using four-wave mixing in fibers

    Page(s): 2696 - 2701
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    Improvement of transmission performance of phase-shift-keying signals by the use of ultrafast optical limiters (amplitude regenerators) based on four-wave mixing (FWM) in fibers is theoretically and numerically studied. Theoretical analysis focuses on the nonlinear phase noise (the Gordon-Mollenauer effect) and its reduction by the limiters. It is shown that the cubic growth of the phase variance as the distance extends can be suppressed by the limiters that are periodically inserted in the system, although some additional phase noise is introduced by them. Numerical simulation is performed for nonreturn-to-zero (NRZ) differential phase-shift-keying (DPSK) transmission in a quasi-linear highly dispersed-pulse system with and without limiters. The results show that the maximum transmission distance is extended by the limiters. A clear indication of nonlinear phase-noise reduction at the high-signal-power regime, however, is not seen. This is attributed to the existence of intrachannel-FWM-induced phase fluctuation, which cannot be effectively suppressed by the amplitude limiter. View full abstract»

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  • Realistic monomode air-core honeycomb photonic bandgap fiber with pockets

    Page(s): 2702 - 2706
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    We present a photonic bandgap calculation of monomode air-core fibers with a realistic treatment of "pocket" interstitials that are formed in a honeycomb cladding. The analytic Fourier transformations of different honeycomb-lattice unit cells are used for plane-wave calculations. The consideration of the true pocket geometry within the cladding shifts the fundamental bandgap to higher frequencies and leads to a hollow-core fiber. The core radius necessary for a monomode fiber is approximated and then proved via the full-vectorial solution. The field distribution and polarization state of the fundamental mode for a real honeycomb photonic-crystal fiber (PCF) are given. View full abstract»

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  • Confinement losses and optimization in rectangular-lattice photonic-crystal fibers

    Page(s): 2707 - 2712
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    Confinement losses in highly birefringent rectangular-lattice photonic-crystal fibers (RLPCFs) are investigated by the multipole method. The losses are strongly polarization dependent, which is due to the anisotropic properties of the cladding. The feature is applied to construct a new kind of single-polarization single-mode photonic-crystal fibers (PCFs), which is based on large differential loss between the two polarizations of the fundamental mode. Furthermore, it is found that the birefringence of RLPCFs is determined mainly by the air holes near the defect core. Consequently, a sandwiching (between triangular structures) rectangular configuration that has the property of reducing leakage loss while simultaneously retaining the birefringence of RLPCF is proposed. View full abstract»

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  • Long-term reliability of single-mode fibers when exposed to high-power laser light

    Page(s): 2713 - 2718
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    The reliability of a pure silica-core single-mode fiber (SCF) and a germanium-doped fiber [dispersion-shifted fiber (DSF)] with long-term exposure to continuous-wave (CW) high-power laser light is reported. It was found that the optical loss in the 0.6-1.6-μm region and the Raman spectra of SCF and DSF remained unchanged after 1900 h of exposure to an 8-W CW laser light and 2000 h of exposure to an 8.5-W CW laser light at 1.48-μm, respectively. The nonbridging oxygen hole center (NBOHC) concentration generated in SCF by 1900 h of exposure is estimated to be below the detection limit of 2×1012 cm-3. SCF and DSF can be expected to exhibit long-term (> 20 years) reliability when exposed to several watts of laser power in the S, C, and L bands in terms of optical degradation due to defect formation via multiphoton absorption. View full abstract»

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  • Three-dimensional analysis of scattering losses due to sidewall roughness in microphotonic waveguides

    Page(s): 2719 - 2732
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    We present a three-dimensional (3-D) analysis of scattering losses due to sidewall roughness in rectangular dielectric waveguides valid for any refractive-index contrast and field polarization. The analysis is based on the volume current method and uses array factors to introduce significant mathematical simplifications to better understand the influence of individual waveguide parameters on scattering losses. We show that the typical two-dimensional (2-D) analyses can substantially overestimate scattering losses in small waveguides and that scattering losses exhibit considerable polarization dependence. We produce scattering-loss estimates for a wide variety of waveguides and provide guidelines for design of waveguide cross sections that are less sensitive to sidewall roughness. View full abstract»

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  • Three-dimensional waveguide arrays for coupling between fiber-optic connectors and surface-mounted optoelectronic devices

    Page(s): 2733 - 2739
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    This paper describes the fabrication of novel surface-mountable waveguide connectors and presents test results for them. To ensure more highly integrated and low-cost fabrication, we propose new three-dimensional (3-D) waveguide arrays that feature two-dimensionally integrated optical inputs/outputs and optical path redirection. A wafer-level stack and lamination process was used to fabricate the waveguide arrays. Vertical-cavity surface-emitting lasers (VCSELs) and photodiodes were directly mounted on the arrays and combined with mechanical transferable ferrule using active alignment. With the help of a flip-chip bonder, the waveguide connectors were mounted on a printed circuit board by solder bumps. Using mechanical transferable connectors, which can easily plug into the waveguide connectors, we obtained multi-gigabits-per-second transmission performance. View full abstract»

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  • Design of photonic-crystal and wire waveguide interface

    Page(s): 2740 - 2745
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    The coupling of light between wire-dielectric and photonic-crystal waveguides, characterized by a triangular lattice of air holes, is investigated through a finite-element time domain (FE-TD) approach, in order to optimize the transmission spectrum. The displacement of the inner-hole rows of the photonic-crystal waveguide, on both sides of the interface, has been shown to considerably improve the coupling, resulting in transmission values higher than 90% and 95% over bandwidths of hundreds of nanometers around 1550 nm. The new design approach is successfully proposed for input and output waveguides with width equal to √3Λ, as well as for larger widths, like 2√3Λ and 3√3Λ, with Λ being the period of the photonic crystal. View full abstract»

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  • Solid immersion lenses in planar waveguides

    Page(s): 2746 - 2748
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    In this paper, solid immersion lenses (SILs) in silicon-based planar waveguides are designed and fabricated. The lenses are designed by the ray-tracing method to optimize the lens profiles. Experimental results show that a minimum spot size of 0.77 μm can be obtained as the calculation prediction. Hence, the SILs combined with other optical components in planar waveguides can alleviate the alignment, tilt, and packaging problems in free-space optical systems. View full abstract»

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  • Guided modes of a width-reduced photonic-crystal slab line-defect waveguide with asymmetric cladding

    Page(s): 2749 - 2755
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    The authors fabricated GaAs-based width-reduced photonic-crystal (PC) slab line-defect waveguides with asymmetric cladding, characterized optically by broadband transmission spectral results. These waveguides were vertically sandwiched between air and oxide claddings. Transmission peaks originating from the guided mode located within the bandgap were observed, thereby showing the presence of a bandgap effect for the transverse-electric (TE)-like guided mode even with the coexistence of a fundamental transverse-magnetic (TM)-like mode. Propagation loss spectra were derived from transmission spectra for both TE and TM polarization inputs. Comparing the obtained spectra to band diagrams, the authors detected a mini-stopband effect in the transmission spectra arising from a folding of the fundamental TM-like mode at the Brillouin zone boundary. The coupling coefficient was then estimated to be ∼0.01 [a-1] (with a being a lattice constant). Dips in spectral intensity were also observed and were attributed to TE-TM mode conversion based on a comparison to the band diagram. View full abstract»

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  • Zero-chirp broadband Z-cut Ti:LiNbO3 optical modulator using polarization reversal and branch electrode

    Page(s): 2756 - 2760
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    In this paper, a novel zero-chirp Z-cut LiNbO3 optical modulator using ferroelectric polarization reversal and a branch electrode is proposed. The optical modulator with a Ti-diffused optical waveguide had a very small chirp parameter, which was less than 0.02. The performance showed a preferable 10-Gb/s eye opening and bias stability. View full abstract»

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  • Spectral characteristics of optical pulse amplification in SOA under assist light injection

    Page(s): 2761 - 2771
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    This paper analyzes the spectral characteristics of optical pulse amplification in semiconductor optical amplifiers (SOAs) with gain and transparent region assist light injection. It is shown that gain region light can decrease the spectral broadening and shifting, while transparent light cannot improve the spectral distortion, though it can accelerate the carrier recovery. The relationships of the frequency peak shift with the amplifier's bias current and length are also given; particular attention is paid to the differences between the co- and counterpropagating configurations. 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