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Lightwave Technology, Journal of

Issue 11 • Date Nov 2002

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Displaying Results 1 - 12 of 12
  • Theory and design of a tapered line distributed photodetector

    Page(s): 1942 - 1950
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (556 KB) |  | HTML iconHTML  

    We present the theory and design of a tapered line distributed photodetector (TLDP). In the previously demonstrated velocity-matched distributed photodetector (VMDP), high electrical bandwidth is achieved by proper termination in the input end to absorb reverse traveling waves, sacrificing one-half of the quantum efficiency. By utilizing the tapered line structure and phase matching between optical waves and microwaves in our analyzed structure, a traveling-wave photodetector is more realizable and ultrahigh bandwidth can be attained due to removal of the extra input dummy load that sacrifices one-half of the total quantum efficiency. To investigate the advantages of TLDP over VMDP, we calculate their electrical bandwidth performances by using an analytic photodistributed current model. We adopted low-temperature-grown (LTG) GaAs-based metal-semiconductor-metal (MSM) traveling-wave photodetectors as example unit active devices in the analytic bandwidth calculation for their high-speed and high-power performances. Both VMDP and TLDP in our simulation are assumed to be transferred onto glass substrates, which would achieve high microwave velocity/impedance and make radiation loss negligible. The simulated bandwidth of a properly designed LTG GaAs MSM TLDP is ∼325 GHz, which is higher than the simulated bandwidth of the LTG GaAs MSM VMDP with an open-circuit input end (∼240 GHz) and is almost comparable to the simulated bandwidth of an input-terminated LTG GaAs MSM VMDP (∼330 GHz). This proposed method can be applied to the design of high-bandwidth distributed photodetectors for radio-frequency photonic systems and optoelectronic generation of high-power microwaves and millimeter waves. View full abstract»

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  • Complete analysis of sideband instability in chain of periodic dispersion-managed fiber link and its effect on higher order dispersion-managed long-haul wavelength-division multiplexed systems

    Page(s): 1895 - 1907
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (949 KB) |  | HTML iconHTML  

    We present for the first time a complete theoretical analysis of sideband instability (SI) that occurs when two kinds of fibers with different characteristics are concatenated to form a dispersion-managed fiber link. In the analysis, the following three cases are taken into account: case (a) when a dispersion-management period is larger than an amplification period, case (b) when the two lengths are equivalent, and case (c) when a dispersion-management period is smaller than an amplification period. We find that the SI gain peak appears at frequencies determined by the larger of the two variation periods. Moreover, for all three cases, the magnitude of the SI gain reduces with the increase in strength of dispersion management. Next, we focus on the fiber link using the combination of standard single-mode fiber and reverse dispersion fiber, which is widely used for simultaneously compensating second- and third-order dispersion. By computer simulation, it is shown that in wavelength-division-multiplexed systems, SI still induces significant degradation in channels located at frequencies where SI induced from other channels arises. By reallocating the channel frequency to avoid the SI frequency, the transmission performance is improved significantly. View full abstract»

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  • Variable second-order PMD module without first-order PMD

    Page(s): 1951 - 1956
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (389 KB) |  | HTML iconHTML  

    We propose a module that generates variable second-order polarization mode dispersion (PMD) without producing any first-order PMD. It is based on four identical fixed differential group delay segments arranged in a symmetrical manner. Only one control parameter varies the magnitude of second-order PMD. View full abstract»

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  • Computation of full-vector modes for bending waveguide using cylindrical perfectly matched layers

    Page(s): 1976 - 1980
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (369 KB) |  | HTML iconHTML  

    A new full-vector approach to calculate leaky modes on three-dimensional bending waveguides is developed and demonstrated with the help of the cylindrical perfectly matched layer (CPML) numerical boundary conditions. By utilizing the complex coordinate stretching technique in the cylindrical system, a new set of full-vector wave equations for the bending waveguide structures are derived for the perfectly matched layer regions. Numerical solutions by the finite-difference schemes for the new wave equations are shown to yield highly accurate complex propagation constants (e.g., the bending-induced phase shifts and leakage losses) and modal field patterns, due primarily to the effective CPML. View full abstract»

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  • Optimal design of an MMI coupler for broadening the spectral response of an AWG demultiplexer

    Page(s): 1957 - 1961
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (386 KB) |  | HTML iconHTML  

    Optimal design of a multimode interference (MMI) coupler for broadening the spectral response of an arrayed-waveguide grating (AWG) demultiplexer is considered. By using a Gaussian beam approximation, an analytical expression for the spectral response of an AWG demultiplexer (with an MMI section) is obtained. A simple analytical formula is derived to relate the optimal MMI length to the separation between the peaks of the twofold images in the MMI region. This peak separation is related to the width of the MMI section. In the proposed design method, a required 1-dB passband width determines the peak separation, which then determines the optimal value for the length of the MMI section according to the analytical formula. The designed flat-top AWG demultiplexer is verified by the beam propagation method. View full abstract»

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  • Effect of modulator chirp and sinusoidal group delay ripple on the performance of systems using dispersion compensating gratings

    Page(s): 1918 - 1923
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (372 KB) |  | HTML iconHTML  

    The implications that the nonideal characteristics of a dispersion compensating grating have on system performance are determined, for the most part, by the group delay ripple (GDR) of the grating response over the modulated signal bandwidth. Since the GDR typically exhibits an irregular variation with wavelength that has periodic features, it is convenient to use a sinusoidal variation to assess the implications on system performance. The portion of the grating bandwidth occupied by the modulated optical signal is determined by the carrier signal wavelength, bit rate, modulation format, and modulator chirp. The implications of modulator chirp on the performance of 10-Gb/s dispersion compensated systems are considered. Using a LiNbO3 Mach-Zehnder modulator, an electroabsorption modulator, and a multiple quantum-well Mach-Zehnder modulator with distinct chirp properties, the results demonstrate that to accurately assess the implications of GDR, the properties of the modulator chirp must be considered. In particular, results for chirp-free optical signals underestimate the implications of the GDR on system performance. View full abstract»

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  • A new transmitter-receiver architecture for noncoherent multirate OFFH-CDMA system with fixed optimal detection threshold

    Page(s): 1885 - 1894
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (714 KB) |  | HTML iconHTML  

    Analyzes a new transmitter-receiver architecture based on a modified version of unipolar-bipolar correlation proposed for a noncoherent multirate optical fast frequency hopping code-division multiple-access (OFFH-CDMA) system. The system assigns a frequency-shifted version (FSV) of the code used to transmit data bit "1" in order to transmit data bit "0." For the original system, we show that due to the nature of the multimedia network, the fluctuation in the multiple-access interference (MAI) average causes a threshold drift and thus an increase in the probability of error. This paper also provides a stochastic description of the MAI average amplitude fluctuation using a predefined multimedia probability density function. A system model is presented; in addition, the signal-to-interference ratio is derived. From the theoretical analysis and numerical results, it is shown that the proposed system has good performance without dynamic estimation of the detection threshold, and thus is independent of both the number of users and the distribution of those users in the offered multimedia classes. View full abstract»

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  • Photonic bandpass filters with high skirt selectivity and stopband attenuation

    Page(s): 1962 - 1967
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (498 KB)  

    A new photonic signal processor topology that simultaneously achieves both a high-Q and a high skirt selectivity and stopband attenuation filter response is presented. It is based on a novel dual-cavity bandpass optical structure in which two pairs of active fiber Bragg grating cavities are used with an optical gain offset to control the poles and stopband attenuation characteristics of the filter. This concept enables a large improvement in the filter stopband attenuation, rejection bandwidth, and skirt selectivity to be realized. Measured results demonstrate both a narrow bandpass bandwidth of 0.4% of center frequency and a skirt selectivity factor of 16.6 for 40 dB rejection, which corresponds to a 6.5-fold improvement in comparison to conventional single cavity high-Q structures. To our knowledge, this is the best skirt selectivity reported for a photonic bandpass filter to date. The new photonic filter structure has been experimentally verified and excellent agreement between measured and predicted responses is shown. View full abstract»

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  • Study of hydrogen diffusion in boron/germanium codoped optical fiber

    Page(s): 1933 - 1941
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (611 KB) |  | HTML iconHTML  

    Presents a novel technique for studying the dynamics of hydrogen diffusion in optical fiber. It shows that the hydrogen contributes directly to the effective refractive index of the fiber by its dielectric susceptibility. It provides a simple theory that relates the refractive index change to the total hydrogen concentration in the fiber core. It also deduces that there is a small contribution of less than 5% to the refractive index through the photoelastic effect. A low-finesse fiber Bragg grating Fabry-Perot interferometer allows the determination of the evolution of the hydrogen concentration in situ. The experimental results obtained for isothermal and isobaric diffusion between 45°C and 90°C yielded values for the parameters of Arrhenius-type expressions for the diffusivity, permeability, and solubility of hydrogen in germanium/boron codoped single-mode fiber. In addition, least squares curve-fits for outdiffusion yielded the gas-phase mass-transfer coefficient as a function of temperature. View full abstract»

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  • Phase dynamics of a timing extraction system based on an optically injection-locked self-oscillating bipolar heterojunction phototransistor

    Page(s): 1924 - 1932
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (711 KB) |  | HTML iconHTML  

    We describe the phase dynamics of a timing extraction system based on direct optical injection locking of a multifrequency oscillator employing an InGaAs/InP heterojunction bipolar phototransistor. We present a general model for the locking range, jitter transfer function, and output phase noise. The model is confirmed by a series of locking experiments. We consider first fundamental timing extraction, that is, a 10-GHz oscillator extracting the clock from a 10-Gbit/s data stream. Second, we address superharmonic timing extraction where 40-Gbit/s data lock the fourth harmonic of the 10-GHz oscillator. In the superharmonic timing extraction case, a clock is extracted at 40 GHz as well as its subharmonics at 10, 20, and 30 GHz. View full abstract»

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  • Polymer micro-ring filters and modulators

    Page(s): 1968 - 1975
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1223 KB) |  | HTML iconHTML  

    Micro-ring wavelength filters and resonant modulators using polymer materials at 1300 nm and 1550 nm are analyzed, designed, and demonstrated. The rings are integrated with vertically coupled input and output waveguides. The devices are fabricated using optical lithography. Filters with a finesse of 141 and free spectral range of 5 nm at 1300 nm and finesse of 117 with a free spectral range (FSR) of 8 nm at 1550 nm are demonstrated. Ring resonators with a Q as high as 1.3 × 105 at 1300 nm are demonstrated. The filters can be temperature tuned at the rate of 14 GHz/°C. Resonant ring modulators, which use an electrooptic polymer, are demonstrated. The resonance wavelength voltage tunes at the rate of 0.82 GHz/V. The modulators have a bandwidth larger than 2 GHz. Using the resonant modulator, and open eye diagram at 1 Gb/s is demonstrated. View full abstract»

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  • Numerical Simulation of a lightwave synthesized frequency sweeper incorporating an optical SSB Modulator composed of four optical phase Modulators

    Page(s): 1908 - 1917
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (572 KB) |  | HTML iconHTML  

    We describe the numerical analysis of a lightwave synthesized frequency sweeper (LSFS) that uses an optical single-sideband (SSB) modulator composed of four optical phase modulators. The SSB modulator realizes a large frequency shift in the LSFS. This means that we can reduce the number of pulse circulations in the LSFS cavity to cover a given frequency sweep range. We propose a frequency-domain analysis method for the LSFS, in which a general optical modulator is expressed by using a matrix that includes optical phase terms. We employ this method to simulate the LSFS for several different phaseand group-velocity dispersion values in the lightpaths in the LSFS cavity. The results indicate that we can realize a linear frequency sweep by adjusting the phase change of the modulation signal during the cavity round-trip time. View full abstract»

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Aims & Scope

The Journal of Lightwave Technology contains articles on current research, applications and methods used in lightwave technology and fiber optics.

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Meet Our Editors

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