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Lightwave Technology, Journal of

Issue 3 • Date March 2003

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Displaying Results 1 - 25 of 36
  • Guest editorial optical MEMS and its future trends

    Page(s): 582 - 583
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    Freely Available from IEEE
  • Tunable spectral slicing filters for dense wavelength-division multiplexing

    Page(s): 837 - 847
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1224 KB) |  | HTML iconHTML  

    A new type of polarization independent guided-wave optical filter with etalon-like spectral response for wavelength-division multiplexing (WDM) is described and analyzed. A four-port integrated optic device performs the spectral slicing (wavelength interleaving/deinterleaving) function of selecting equally spaced frequency channels from a group of incident WDM channels. Spectral selection is based upon codirectional transverse electric (TE)/spl harr/transverse magnetic (TM) conversion induced by N equally spaced coupling regions in a single mode optical waveguide. A matrix formulation is used to determine the TE/spl harr/TM coupling strengths which yield N-1 equally spaced nulls between adjacent selected frequencies, for N as high as 16. Spectral response is calculated for polarization coupling regions of infinitesimal length as well as for polarization coupling induced by gratings of finite extent. Lithium niobate, due to its high birefringence, is an ideal substrate material for dense WDM filters. Polarization coupling can be induced by a sparse grating of an overlay material such as fused silica. The spectral response can be tuned at submicrosecond speeds by an applied electric field which alters the waveguide birefringence, and hence the optical frequency at which near-complete polarization conversion occurs. A reflective design to make more effective use of the available substrate dimension is described. Single channel selection over a wide spectral range can be achieved by cascading two of the filters in series. View full abstract»

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  • Time-multiplexed signals and parallel signal analysis/switch optimization for MEMS-based optical cross-connect

    Page(s): 609 - 613
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (356 KB) |  | HTML iconHTML  

    The calibration of the numerous mirror pairs, or switches, in MEMS-mirror optical cross-connect systems is a critical process in their manufacture. Because the number of switch connections for these systems scales quadratically to the number of inputs/outputs, this places great demands on the equipment used to perform testing. We propose and demonstrate a calibration technique for generic optical subsystems based on optical time-division multiplexing (OTDM). View full abstract»

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  • Optical CDMA with time hopping and power control for multimedia networks

    Page(s): 695 - 702
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (494 KB) |  | HTML iconHTML  

    Optical code-division multiple access (OCDMA) for high-speed multimedia transmission is proposed and its performance is investigated. The proposed system introduces time hopping to vary transmission bit rate and power control to control transmission signal performance, which allows various signals with different desired rate and performance. An expression for the bit error rate (BER) of the proposed system is derived and numerical results are shown. An optical power selector (OPS) coupled with a hard limiter are also proposed to improve system performance. The OPS is a device to transmit the instantaneous maximum optical power among input signals. The OPS combined with the optical hard limiter reduces the interference from simultaneous users which results in an improved BER. BER is theoretically derived and numerical results for some parameters are shown. We show that the proposed system significantly improves BER and is an attractive scheme for future multimedia networks. View full abstract»

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  • Optoelectromechanical switch array with passively aligned free-space optical components

    Page(s): 664 - 671
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    An all-optical switch array with micro mirrors driven by electrostatic micro motors has been developed in a LIGA-technique. The system has been designed for single mode application at the telecommunication wavelength of 1.55 μm. All fixed optical components are passively aligned inside a LIGA-structured micro optical bench. The signals are detoured inside the optical bench by means of micro mirrors, which are attached to micro wobble motors. In order to avoid angular displacements of the deflected light beams double mirrors are used. First, prototypes with 2 input and output ports have been realized. Two of these 2 × 2 switch matrices have been integrated on a 10 × 10 mm2 ceramic substrate with six micro motors of 1.7 mm diameter. Switching times down to 30 ms have been achieved. The crosstalk between different channels is 90 dB. The insertion loss with passive alignment of the optical elements yielded 3 dB with a repeatability better than ±0.3 dB. View full abstract»

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  • Assessment of laser noise influence on direct-detection transmission system performance

    Page(s): 759 - 768
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    A new semi-analytical method of estimating the influence of laser noise on directly modulated direct-detection transmission system performance is proposed. Its accuracy is assessed for different propagation situations and receiver noise type dominance using rigorous mixed semi-analytical simulation. Two different relative intensity noise (RIN) powers at receiver input associated with the two laser currents of the binary levels are considered, and not just a single one corresponding to the laser average current as in other published works. It is shown that, to perform rigorous simulation, suitable methods of solving stochastic laser rate equations should be used, and a number of samples high enough in order to stabilize the sensitivity estimator should be considered. It has been found that, for power penalties of about 1 dB, more than 150 samples may be necessary. For a power penalty due to laser noise of about 4.5 dB, discrepancies not exceeding 0.4 dB are observed between the results obtained using the new semi-analytical approach and using the rigorous simulation. It is shown that the new semi-analytical approach gives more precise results than other approach currently used. For a power penalty due to laser noise not exceeding 2 dB, the discrepancies between the two approaches can reach roughly 1 dB. It is shown that these discrepancies can increase with the laser linewidth. Explicit expressions for system power penalty due to the RIN at the fiber output are presented, for both signal-independent and -dependent noise dominance. It is shown that these expressions give good upper bounds of the real power penalties. View full abstract»

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  • Electromagnetic micromirror array with single-crystal silicon mirror plate and aluminum spring

    Page(s): 584 - 590
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    We have designed and fabricated an addressable 4 × 4 array of micromirrors capable of providing up to 90° of angular deflection. Each micromirror comprises a single-crystalline silicon mirror plate supported by aluminum springs, which provides an extremely flat reflective surface and a compliant spring material that enables the integration of the device into a limited area without mitigating its performance (i.e., total angular deflection). The device is fabricated using a combination of surface and bulk micromachining processes, such as electroplating, bulk wet etching and XeF2 etch processes. Selective actuation is accomplished by the use of an electrostatic clamping force on each mirror plate. A mirror rotation angle of more than 80° can be obtained by applying an external magnetic field, and this angle can be further increased by the use of an electrostatic force. The designed structure can be used in microphotonic applications. View full abstract»

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  • Reconfigurable π-shifted and Mach-Zehnder bandpass filters on the basis of electrooptically induced long-period gratings in a planar waveguide

    Page(s): 854 - 861
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    The concept of a reconfigurable band-stop filter on the basis of an electrically induced long-period grating in a waveguide with an electrooptic core is extended to the design of reconfigurable bandpass filters through introduction of π-shift or splitting a grating into two sections that form a Mach-Zehnder (MZ) interferometer. In the proposed design, a single or multiple π-shifts can be easily introduced as well as easily removed in any place along the grating by simply reversing the applied voltage polarity for a portion or portions of the interdigitated electrode (IDE) fingers. On other hand, because coupling does not occur without the presence of the voltage at the finger(s), an MZ interferometer can be easily created, modified, and removed by grounding a number of IDE fingers inside the grating. On the basis of this concept, bandpass transmission characteristics are studied for the gratings with a single π-shift, multiple π-shifts, and MZ interferometers for an arbitrary number of the grounded IDE fingers. View full abstract»

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  • Phase-shifted transmission/reflection-type hybrid extrinsic Fabry-Perot interferometric optical fiber sensors

    Page(s): 797 - 804
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (678 KB) |  | HTML iconHTML  

    Conventional interferometric optical fiber sensors, including the extrinsic Fabry-Perot interferometric (EFPI) optical fiber sensor, have the drawback of ambiguous measurement directions and direction changes, because their signal processing using only fringe counting cannot present measurement direction information, such as tension/compression of strain or increment/decrement of temperature. An EFPI optical fiber sensor constructed with a transmission-type structure (TEFPI optical fiber sensor) can successfully compensate for this problem. However, it has low interferometric fringe visibility and requires somewhat sophisticated signal processing to detect the measurement direction changes. In this research, a hybrid EFPI optical fiber sensor is presented from which transmission-type and reflection-type sensor signals can be simultaneously acquired. The linear combination of the actual transmission-type and reflection-type signals is shown to have a shifted phase from the reflection-type signal according to measurement directions, and thus the phase behavior of lead/lag can present the measurement direction information. Because the hybrid sensor uses separated signals for the measurement quantity and direction, its signal processing is more robust than that of the TEFPI sensor. The sensor and signal processing algorithm were verified with the strain measurement experiments. View full abstract»

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  • A unified study of contention-resolution schemes in optical packet-switched networks

    Page(s): 672 - 683
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    This paper presents a comprehensive study of contention-resolution schemes in a multiwavelength optical packet-switched network. This investigation aims to provide a unified study of a network of optical routers, which include contention resolution in wavelength, time, and space dimensions. Specifically, we show: 1) how to accommodate all three dimensions of contention resolution in an integrated optical router; 2) how the performance of the three dimensions compare with one another; and 3) how various combinational schemes can be designed and how they perform. With the representative architectures and network topologies studied in this paper, the simulation experiment results capture the characteristics of different contention-resolution schemes, and they quantify the upper-bound average offered transmitter load for these schemes. The combinational contention resolution schemes are shown to effectively resolve packet contention and achieve good network performance under light to intermediate load. View full abstract»

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  • Amplification properties of Er3+-doped photonic crystal fibers

    Page(s): 782 - 788
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    The amplification properties of different photonic crystal fibers have been studied by means of a full vector finite-element modal formulation combined with a population and propagation rate equation solver. A honeycomb as well as a cobweb photonic crystal fiber have been considered. The consequences of the defect dimension and the dopant radius on the field intensity distribution as well as the overlap integrals have been analyzed. Results demonstrate that a proper photonic crystal fiber design can be usefully exploited in order to obtain active fibers with superior characteristics compared to standard step index ones. In particular, photonic crystal fibers open up the possibility of a gain medium with highly flexible geometric, dispersion, and amplifying characteristics. View full abstract»

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  • An integrated laser blood flowmeter

    Page(s): 591 - 595
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (540 KB) |  | HTML iconHTML  

    We have constructed a very small and lightweight blood flowmeter using micromachining and surface mounting techniques for a wearable health monitoring system. The hybrid integrated structure of the optical system incorporates a InGaAsP-InP distributed feedback laser diode (DFB-LD) with a wavelength of 1310 nm, an edge-illuminated photodiode (PD) and a polyimide waveguide on silicon substrate (2 mm × 3 mm). This integrated flowmeter can be positioned directly on the tissue and permits real-time monitoring of capillary microcirculation. In-vivo measurements of blood perfusion in a finger confirm the feasibility of the blood flowmeter. View full abstract»

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  • N×N multiwavelength optical cross-connect based on tunable fiber Bragg gratings

    Page(s): 703 - 718
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (962 KB) |  | HTML iconHTML  

    We propose a highly channel-scalable multiwavelength optical cross-connect (OXC) based on tunable fiber Bragg gratings (TFBGs), which is suited for metropolitan or access networks. N×N OXC of this architecture is constructed by cascading independently operating routing modules, and each routing module consists of fiber Bragg gratings (FBGs) with fixed center wavelength and a TFBG-based N×N routing block. The group velocity dispersion (GVD) and intraband crosstalk (IXT) are the main signal-degrading factors arising from the operation of the proposed OXC, and the effectiveness of each factor is individually investigated numerically for 10-Gb/s nonreturn-to-zero (NRZ) systems. Then, a routing experiment of the proposed OXC is carried out in a 3×3 routing block configuration, using OC-192 signals with channel spacing of 0.8 nm. Finally, the installable size of the proposed OXC and network scale are estimated by resorting to a comprehensive numerical simulation of 10-Gb/s NRZ signal transmission. View full abstract»

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  • A modified imaginary distance BPM for directly computing arbitrary vector modes of 3-D optical waveguides

    Page(s): 862 - 867
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    A method for the direct calculation of arbitrary vector modes of three-dimensional optical waveguides is presented. The proposed mode-solving scheme, based on a modified imaginary distance beam propagation method, provides an easy to implement explicit algorithm. A finite-difference discretization is used in the transverse plane and a Chebyshev approximation in the propagation direction. Approximate values of the propagation constants of the modes to be calculated are required and it is demonstrated that this data can be obtained in an efficient way by using the least squares Prony method. View full abstract»

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  • Beam-steering micromirrors for large optical cross-connects

    Page(s): 634 - 642
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1132 KB) |  | HTML iconHTML  

    This paper describes Si-micromachined two-axis beam-steering micromirrors and their performance in 256 × 256- and 1024 × 1024-port large optical cross-connects (OXCs). The high-reflectivity wavelength-independent mirrors are electrostatically actuated; capable of large, continuous, controlled, dc tilt in any direction at moderate actuation voltages; and allow setting times of a few milliseconds. Packaged two-dimensional (2-D) arrays containing independently addressable identical 256 and 1296 mirrors are used to build fully functional bitrate and wavelength-independent single-stage, low-insertion-loss, single-mode fiber OXC fabrics. View full abstract»

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  • An optimization model for placement of wavelength converters to minimize blocking probability in WDM networks

    Page(s): 684 - 694
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (805 KB) |  | HTML iconHTML  

    The introduction of wavelength converters in wavelength division multiplexing (WDM) networks can reduce the blocking probabilities of calls. In this paper, we study the problem of placing a given number of converters in a general topology WDM network such that the overall system blocking probability is minimized. The original contributions of this work are the following: 1) formulation of success probability in a network as a polynomial function of the locations of converters; 2) proposal of an optimization model of the converter placement problem as the minimization of a polynomial function of 0-1 variables under a linear constraint, so that standard optimization tools can be employed to solve the problem; and 3) design of a search algorithm that can efficiently find the optimal solution to the converter placement problem. Experiments have been conducted to demonstrate the effectiveness of the proposed model and the efficiency of the algorithm. View full abstract»

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  • Numerical study of random variations of span lengths and span path-average dispersions on dispersion-managed soliton system performance

    Page(s): 769 - 775
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    We have studied the performance of dispersion-managed (DM) soliton systems with random variations of span lengths and span path-average dispersions by numerical simulation. We show that while DM solitons still exist in systems with nonperiodic dispersion maps, those nonperiodic maps tend to degrade system performance. We investigate the performance degradation of both on-off keyed and differential phase-shift keyed DM-soliton systems with random span lengths and random span path-average dispersions. We find that the impairment caused by the span path-average dispersion variation is larger than that caused by the span length variation, and that the reduction in quality factor due to the span length and the span path-average dispersion variations is less in dense wavelength-division multiplexing (WDM) than in single-channel transmission systems. In addition, we also show that keeping the overall path-average dispersion constant within a few spans can reduce the random dispersion map-induced performance degradation. View full abstract»

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  • Design and implementation of wavelength-flexible network nodes

    Page(s): 648 - 663
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1413 KB) |  | HTML iconHTML  

    This paper analytically and experimentally examines node architectures for wavelength-routing networks, with emphasis on the degree of wavelength conversion provided. Wavelength flexibility simplifies network management and increases network capacity but requires large cross-connects and deployment of wavelength converters (WCs). A simple probabilistic model is used to upper-bound the number of WCs required at a network node, under dynamic traffic load. When provisioned in a shareable pool, with a fixed number of wavelength channels per fiber, the number of WCs required remains low as overall network capacity is scaled up. Motivated by this analysis, experiments demonstrate the feasibility of implementing wavelength-flexible network nodes using large microelectromechanical (MEMS)-based cross-connects and all-optical WCs. In one design, WCs were attached directly to cross-connect output ports, and in another, they were attached in a loop-back fashion to allow sharing. Error-free transmission at 10 Gb/s was demonstrated in both cases. View full abstract»

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  • Performance characterization of high-bit-rate optical chaotic communication systems in a back-to-back configuration

    Page(s): 750 - 758
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    A comparative study of three data-encoding techniques in optical chaotic communication systems is reported. The chaotic carrier is generated by a semiconductor laser subjected to optical feedback and the data are encoded on it by chaotic modulation (CM), chaotic masking (CMS), or chaotic shift keying (CSK) methods. In all cases, the receiver-which is directly connected to the transmitter-consists of a semiconductor laser similar to that of the transmitter subjected to the same optical feedback. The performance of this back to back configuration is numerically tested by calculating the Q-factor of the eye diagram of the received data for different bit rates from 1 to 20 Gb/s. The CM scheme appears to have the best performance relative to the CMS and CSK scheme, before and after filtering the residual high-frequency oscillations remaining due to nonperfect synchronization between the transmitter and receiver. Moreover, in all encoding methods, a decrease in the Q-factor is observed when the repetition bit-rate of the encoding message increases. In order to achieve as high Q-factor values as possible, a well-synchronized chaotic master-slave system is required. View full abstract»

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  • Novel optical fiber cable for feeder and distribution sections in access network

    Page(s): 789 - 796
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    This paper describes a new termination, feeder and aerial distribution cable for the feeder and distribution sections of access networks. These cables have great advantages in terms of cost and installation workability that will enable us to realize fiber-to-the-home (FTTH). First, we describe the cable requirements with regard to cost reduction and installation. Based on the requirements, we investigated and optimized the structural design of these cables. We manufactured these cables according to the results and confirmed that their transmission and mechanical characteristics are sufficiently stable for them to be used in access networks for FTTH. View full abstract»

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  • Photolithographic processing of hybrid glasses for microoptics

    Page(s): 614 - 623
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1757 KB) |  | HTML iconHTML  

    Hybrid glass materials are used in the photolithographic fabrication of optical and optomechanical structures. Two different photolithographic hybrid glass processing methods are described. The first one is referred as photolithographic patterning and the second as direct photolithographic deforming of hybrid glass materials. No etch transfer of the photoimaged structures is needed. In the latter method even the chemical development step can be excluded from the fabrication. Fabrication of lens-arrays, gratings and other binary structures is presented. The synthesized hybrid glass materials feature minimum optical transmission of 97% at wavelengths ranging from 450 nm to 1600 nm and refractive index of, e.g., 1.53 at 632.8 nm. The photolithographic patterning resulted in structure heights in excess of 180 μm with rms surface roughness values ranging from 10 to 45 nm. The direct photolithographic deforming resulted in structure heights in excess of 27 μm with rms surface roughness values ranging from 1 and 15 nm. View full abstract»

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  • New method to calculate mode conversion coefficients in SI multimode optical fibers

    Page(s): 776 - 781
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (420 KB) |  | HTML iconHTML  

    A simple method is proposed for the experimental calculation of the mode conversion coefficients in multimode optical fibers. It only requires observing the far-field output pattern from a fixed length of fiber as the launching angle changes, as well as the intersection point between two far-field output patterns corresponding to two different input angles. The results obtained with this method are quite insensitive to small variations of the experimental parameters. A good agreement between theoretical and experimental results is also found. View full abstract»

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  • A modular fabrication concept for microoptical systems

    Page(s): 643 - 647
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    A modular fabrication concept is used to build microoptical systems for commercial application. The concept is based on the fact that microoptical systems can be divided into two functional units, the optical and the electrooptical base plate, which covers active optical elements. In the case of defined interfaces, highly specialized manufacturers can fabricate both components separately. A third company will use these components to build the electrooptical subsystem, which is sold as an OEM system to the system manufacturer. Especially for the component fabrication, the equipment costs can be shared among different applications, which makes the component for each application cheaper. A microoptical distance sensor and a microspectrometer for the near-infrared have demonstrated the concept. View full abstract»

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  • Optical orthogonal codes with large crosscorrelation and their performance bound for asynchronous optical CDMA systems

    Page(s): 735 - 742
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    Optical orthogonal codes (OOCs) are commonly used as signature codes for optical code-division multiple-access (OCDMA) communication systems. Many OOCs have been proposed and investigated. Asynchronous OCDMA systems using conventional OOCs have a very limited number of subscribers and few simultaneous users. Recently, we reported a new code family with large code size by relaxing the crosscorrelation constraint to 2. In this paper, by further loosening the crosscorrelation constraint, we adopt the random greedy algorithm to construct a code family which has larger code size and more simultaneous users. We also derive an upper bound of the number of simultaneous users for a given code length, code weight, and bit error rate. The study shows that it is possible to have codes approaching this bound. 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