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Lightwave Technology, Journal of

Issue 1 • Date Jan 2002

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Displaying Results 1 - 16 of 16
  • Performance and modeling of advanced Ti:LiNbO3 digital optical switches

    Page(s): 92 - 99
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (172 KB)  

    High-performance Y-branch digital optical switches realized in Ti:LiNbO3 are presented. Their switching response functions have been optimized in terms of switch voltage and crosstalk ratio. The optimization is based on analyzing different types of waveguide shaping and switching arrangements using coupled mode theory and computer simulations. Excellent switching characteristics are achieved with devices exploiting a specially shaped waveguide branch in a dilated switch arrangement. Demonstrated performances include switching voltage as low as 9 V with crosstalk suppression better than 45 dB and fiber-to-fiber losses as low as 4 dB. Polarization independence with crosstalk suppression better than 40 dB over a 1520- to 1570-nm wavelength range is achieved for any applied switch voltage greater than 18 V. These optimized digital optical switches have further demonstrated the capability to reshape electrical input signals at switching rates of several hundred megahertz View full abstract»

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  • LiNbO3 optical waveguides formed in a new proton source

    Page(s): 71 - 77
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (163 KB) |  | HTML iconHTML  

    Proton-exchanged planar waveguides have been fabricated on Z-cut and X-cut lithium niobate crystals by using a new proton source formed by a mixture of benzoic and adipic acids. Waveguide index profiles and optical characteristics have been obtained at different values of the adipic-benzoic acid concentration ratio. The samples have been structurally characterized by Raman and infrared (IR) absorption spectroscopy and double-crystal X-ray diffraction. Good quality samples have been fabricated by using 30 mol% ratio dilution, showing very low scattering levels (<0.1 dB/cm), relatively high electrooptic coefficient (r33=0.88 pm/V), and low relative percentage of interstitial protons (26%). The main factor limiting the waveguide optical properties is the substitutional-interstitial proton ratio, which can be easily controlled to produce good quality waveguides. A demonstration of the repeatability of the exchange process in the acid mixture is also provided View full abstract»

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  • Intrusion-alarmed fiber optic communication link using a planar waveguide bimodal launcher

    Page(s): 10 - 18
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (149 KB)  

    This paper summarizes the results of our study of a point-to-point, intrusion-alarmed, graded-index, multimode optical fiber communication system. In this intrusion-alarmed system, data light is transmitted in the lowest order modes of a graded-index multimode fiber and intrusion alarm monitor light is simultaneously transmitted in high-order modes. An attempted intrusion to extract data light by bending the fiber results in attenuation of the monitor light in high-order modes, thereby sounding an alarm at the receiver. However, the data light in the fundamental mode, or in the lowest order modes, propagates along or near the fiber axis where the refractive index is highest and is exceptionally difficult to extract from the fiber. Even for severe bending of the fiber, light in the lowest order modes remains trapped in a set of lowest order modes. Additional benefits of data light transmitted in the lowest order modes are capabilities for wider bandwidths and lower modal noise. The performance of four fabricated planar waveguide bimodal launchers for simultaneously launching data light into the fundamental mode, or into the lowest order modes, and monitor fight into high-order modes of graded-index multimode fiber is described. The configuration, construction, and performance of a laboratory prototype alarmed system are described View full abstract»

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  • A wide-angle X-junction in polymer using truncated-structural branches (TSB)

    Page(s): 86 - 91
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (216 KB)  

    We present a detailed design and characterization for a compact X-junction we proposed recently. Even at a wide full-branching angle of 1.4°, simulation predicts the crosstalk and insertion loss to be -20.1 and 0.2 dB, respectively; the wavelength bandwidth is 230 nm (1390-1620 nm). Devices made in polymer realize -16.1-dB crosstalk and 0.3-dB loss View full abstract»

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  • Accurate Q-factor estimation of optically amplified systems in the presence of waveform distortions

    Page(s): 19 - 27
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (271 KB) |  | HTML iconHTML  

    We present an accurate method for the Q-factor estimation even in the presence of waveform distortions in optically amplified systems. The method stands on the assumption that the dominant noises over the bit error rate (BER) are those superimposed on the nearest rails to the decision level. It is clarified that the assumption is usually satisfied. The results also show that, in numerical system evaluation, we should evaluate not only the eye opening but also the probability of occurrence of the rail level View full abstract»

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  • Reflection-type optical waveguide switch with bow-tie electrode

    Page(s): 65 - 70
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (116 KB) |  | HTML iconHTML  

    Based on the total internal reflection and the plasma dispersion effect of SiGe alloy, an intersectional rib optical waveguide switch with bow-tie electrode has been proposed and fabricated for operating wavelengths of 1.3 and 1.55 μm. The thickness of the SiGe layer is 2.6 μm and the width is 9 μm. The branch angle of the switch is 2° and the bow-tie angle is 1.5°. The crosstalks are -19.6 dB for 1.3 μm and -21.8 dB for 1.55 μm. At both wavelengths, the extinction ratio is larger than 38.5 dB and the insertion loss is less than 1.70 dB. The switching time is about 180 ns View full abstract»

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  • Noise limits in reconstruction of optical parameters of silica-based double-layer planar waveguides on silicon

    Page(s): 114 - 119
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (238 KB) |  | HTML iconHTML  

    The paper presents a study on the reliability and limits of the downhill simplex algorithm used to reconstruct optical parameters of double-layer silica waveguides from the measured effective indexes. It provides a number of surface plots of the merit function and explains the behavior of the algorithm in practical situations where the measured effective index data are affected by noise View full abstract»

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  • A grating-based OCDMA coding-decoding system incorporating a nonlinear optical loop mirror for improved code recognition and noise reduction

    Page(s): 36 - 46
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (284 KB) |  | HTML iconHTML  

    We demonstrate an elementary grating-based optical code division multiple access (OCDMA) code generation and recognition system incorporating a nonlinear optical loop mirror (NOLM) within the receiver. We show that the NOLM can act as a nonlinear processing element capable of reducing both the pedestal associated with conventional matched filtering and the width of the associated code-recognition pulse. The pedestal rejection allows for an improved code recognition signal-to-noise ratio (SNR) relative to simple matched filtering alone, and reduced intra- and interchannel interference noise due to code overlap. The system benefits of using the NOLM are experimentally demonstrated under both single- and multiuser operation within a variety of seven- and 63-chip 160-Gchip/s code generation, recognition, and transmission experiments based on the use of bipolar superstructure fiber Bragg grating (SSFBG) coding-decoding pairs. Incorporation of the NOLM is shown to allow error-free penalty-free operation at data rates as high as 2.5 Gb/s under single-user operation, and to provide error-free performance with reduced power penalty in two-user experiments. The narrowed pulse recognition signature offers major advantages in terms of the further all-optical processing of decoded signals, such as code regeneration and recoding View full abstract»

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  • Light-induced self-writing effects in bulk chalcogenide glass

    Page(s): 78 - 85
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (246 KB) |  | HTML iconHTML  

    A waveguide can be self-written by a beam of light propagating in a photosensitive material. We report the first observation of self-writing effects in bulk chalcogenide glass and investigate the influences of different writing beam sizes and powers. We observe increases in refractive index of 2.5×10-4 due to illumination at 1047 nm in Ce-doped Ga-La-S. Simulations of the self-writing process show a good agreement with the experimental results. This verifies our numerical model and allows the dynamics of this process to be explored. Using this knowledge, we predict the experimental parameters and conditions required to write waveguides, tapers, and ultimately complex three-dimensional (3-D) structures View full abstract»

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  • An inverse algorithm to calculate the refractive index profiles of periodically segmented waveguides from the measured near-field intensities

    Page(s): 58 - 64
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (140 KB) |  | HTML iconHTML  

    In this paper, the refractive index profiles of the periodically segmented waveguides (PSWs), which are fabricated in soda-lime glasses by the K+-Na+ ion-exchanged technique, are reconstructed from the measured transmitted near-field (NF) intensity combined with an inverse method. Through the proposed inverse method, the model Δn'=ηΔn, which characterizes the behavior of the PSWs, is also verified. In the numerical process, a finite-difference method is used to discretize the governing equation, and then a linear inverse model is constructed to identify the unknown refractive index profiles. The approach used is to rearrange the matrix form of the governing differential equation and estimate the unknown index profiles of the waveguides. Then, the linear least-squares error method is adopted to find the solutions. The results show that the accuracy of index determination can be accessed even when the measured noise is considered. In contrast to the traditional approach, the advantages of this method are that no prior information is needed on the functional form of the unknown index profiles, no initial guesses are required, no iterations in the calculating process are necessary, no intensity smoothing is required in advance, and the inverse problem can be solved in a linear domain. Furthermore, the existence and uniqueness of the solutions can easily be identified View full abstract»

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  • Active semiconductor microdisk devices

    Page(s): 105 - 113
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (226 KB)  

    The design of active semiconductor microdisk switches, modulators, or wavelength routers enabled by modulating the transfer characteristics of a resonant cavity is investigated. A simple theoretical model based on coupled-mode theory is used to elucidate design trends and constraints in the cases where electroabsorption, gain, and free carrier injection are employed to modulate the resonator characteristic View full abstract»

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  • Dynamics of the chirped return-to-zero modulation format

    Page(s): 47 - 57
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (232 KB) |  | HTML iconHTML  

    We numerically simulated long-distance, high-bit-rate, wavelength division multiplexed (WDM) transmission in dispersion-managed systems. We investigated return-to-zero (RZ) and nonreturn-to-zero (NRZ) modulation formats with amplitude and phase modulation. Consistent with earlier experiments, we find that the chirped return-to-zero (CRZ) modulation format has significant advantages over the NRZ modulation format in WDM systems. We elucidate the physical reasons for these advantages. We then discuss, in detail, the dynamics of the CRZ systems, carefully distinguishing noise effects, single-channel nonlinear effects, and multichannel nonlinear effects. In this way, we provide a physical basis for understanding CRZ systems that should prove useful for future system design. In particular, we find that the pulse evolution is dominated by linear dispersion and that the spread in the eye diagrams is dominated by signal-spontaneous beat noise, just like in linear systems. However, we also find that symmetric dispersion compensation performs better than asymmetric dispersion compensation, due to the effects of nonlinearity. Additionally, we find that interchannel nonlinearities spread the eye diagrams without changing the dynamical behavior. Thus, the system is quasilinear in the sense that its properties resemble those of linear systems, but nonlinearity plays an important role View full abstract»

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  • Variation in the performance of multispan 10-Gb/s systems due to the group delay ripple of dispersion compensating fiber Bragg gratings

    Page(s): 28 - 35
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (200 KB) |  | HTML iconHTML  

    The variation in the performance of multispan lightwave systems that use dispersion-compensating fiber Bragg gratings (FBGs) is characterized in terms of the peak-to-peak group delay ripple over the -1dB bandwidth of the gratings. The irregular dependence of the group delay ripple on wavelength, and the variability in the properties of the group delay ripple for nominally identical gratings make it difficult to predict the overall reflection spectrum for a cascade of gratings. The uncertainty in the overall spectrum must be considered in the system design process. By considering 2401 distinct configurations for the gratings in a four-span 320-km system, simulation results are presented that specify the requirement for the group delay ripple in order for the system performance to remain within a specified penalty View full abstract»

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  • Broad-area diode lasers with plane-mirror and phase-conjugate feedback

    Page(s): 100 - 104
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (91 KB) |  | HTML iconHTML  

    The output state of a broad-area diode (BAD) laser with phase conjugate feedback (PCF) from Rh:BaTiO3 crystal is compared to the same diode laser with conventional optical feedback from a plane mirror. A number of distinct output states, including low frequency fluctuations, are observed for each feedback type. Stable single spectral mode output is achieved with phase conjugate feedback above an injection current dependent critical level (~20%). Conventional optical feedback from a plane mirror does not induce single-mode output at any feedback level View full abstract»

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  • Proposal of a wavelength-selective switch based on an MMIMZI configuration with wavelength-selective phase-tuning circuits

    Page(s): 120 - 125
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (159 KB)  

    This paper proposes a novel photonic device for wavelength-selective switching. The device is based on a multimode-interference Mach-Zehnder interferometer (MMIMZI) configuration with wavelength-selective phase-tuning circuits (WSPTC). Mode propagation theory is used for the analysis of this device View full abstract»

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  • Design-dimensioning model for transparent WDM packet-switched irregular networks

    Page(s): 1 - 9
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (202 KB)  

    A detailed analytical traffic model for all-optical wavelength division multiplexing (WDM) photonic packet-switched networks is presented and the requirements for buffer size and link dimensions are analyzed. This paper shows that due to the topology, packets may generate traffic bottlenecks produced by a tendency of the routing scheme to send packets with different destinations through preferred paths. This effect increases the traffic load and, hence, the probability of blocking at the output links of specific routers in the network and, therefore, a large buffer depth or an increment in the number of fibers per link is required. Three router architectures are analyzed and it is shown that WDM all-optical router architectures with shared contention resolution resources are the best candidates to reduce hardware volume and cost of all-optical networks. It is shown that routers with a bank of completely shared wavelength converters (WCs) require a fraction of WCs compared to router architectures that use a WC per wavelength. This fraction depends on the location of the router, the network topology, and the traffic load in the network. However, in general terms, about 50% to 90% of WCs can be saved by architectures with shared wavelength-conversion resources. Also, it is shown that limited wavelength conversion degrees d=8 and d=10 in packet-switching routers with 16 and 32 wavelengths give the same probability of packet loss performance as full wavelength conversion 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