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Lightwave Technology, Journal of

Issue 5 • Date May 1986

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Displaying Results 1 - 15 of 15
  • [Front cover and table of contents]

    Page(s): 0
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    Freely Available from IEEE
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  • [Back cover]

    Page(s): c4
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    Freely Available from IEEE
  • Low-threshold current AlGaAs/GaAs-distributed feedback laser grown by two-step molecular beam epitaxy

    Page(s): 507 - 512
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    AlGaAs/GaAs-distributed feedback (DFB) lasers with oxide-stripe structure were fabricated by a two-step molecular beam epitaxial (MBE) growth for the first time. The large coupling coefficient of 90 cm-1and the threshold current as low as 165 mA at room temperature were obtained with the second-order gratings. The characteristic temperature T0was as high as 210 K. Single longitudinal-mode oscillation was observed up toI/I_{th} = 1.5and from 0 to 50°C without any mode hopping. The wavelength variation from device to device was ±5 Å. The dependence of the coupling coefficient on the device structure was calculated, and it was shown that MBE is much more advantageous than LPE to enhance the coupling coefficient. View full abstract»

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  • Signal-to-noise ratio in Raman active fiber systems: Application to recirculating delay lines

    Page(s): 560 - 566
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    An analysis of photon count statistics of noise in Raman fiber amplifiers and passive optical components is presented. The resuits are used for evaluating the output signal-to-noise ratio (SNR) of Raman active recirculating delay lines. It is found that the quadratic dependence of the noise on the number of recirculations causes the SNR to decay with increasing optical delays. Ultimate system performance capabilities, as determined by the SNR quantum limit, are discussed. View full abstract»

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  • Bandwidth characteristics of optical transmission line constructed with short-length optical fibers

    Page(s): 530 - 537
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    This paper clarifies the bandwidth characteristics of a VAD-fabricated optical line constructed with short-length optical fibers. The refractive index profiles of these optical fibers are slightly distorted from the ideal profile. Their bandwidth characteristics are calculated and measured under the overfill mode distribution (OMD) and the equilibrium mode distribution (EMD) excitations. As a result, some of the optical fibers are shown to have extremely narrow bandwidths at the short fiber length under OMD excitation as compared with those under EMD excitation. The concatenation factor of the optical line consequently becomes a smaller value than that of an optical line constructed with long-length optical fibers. In addition, the measurement results of the optical subscriber transmission line field trial are shown to be in good agreement with those obtained in this paper. View full abstract»

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  • Improved electrode geometry for electrooptic frequency translation in a channel waveguide

    Page(s): 481 - 489
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    The technique of optical frequency translation by a rotating electric field in a trigonal electrooptic crystal has been adapted to a buried channel waveguide structure. To implement the field rotation under the constraints of a planar geometry, an electrode configuration was adopted consisting of three coplanar, collinear metal strips driven in phase quadrature, with the light guide under the central strip. Elimination of a cyclic modulation of field amplitude, characterizing the results of a previous study by the author, was achieved by appropriately widening the outer electrodes relative to the central one and by choosing a suitable channel depth. Spurious sidebands previously generated by an effective counter-rotating field component are thus removed. It is shown that with a residual modal birefringence equivalent tolambda/20-differential phase retardation, the device here described can achieve 98 percent translation into the single first-order sideband with less than 0.5 percent combined spurious carrier and second-order upper sideband. View full abstract»

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  • InGaAsP ridge waveguide distributed feedback lasers operating near 1.55 µm

    Page(s): 520 - 529
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    Fabrication and performance of ridge waveguide distributed feedback lasers grown by liquid phase epitaxy for operation in the 1.50-1.58 μm spectral region have been studied. These lasers incorporate first- and second-order diffraction gratings written by the electron beam lithography and optical holography and defined by wet chemical etching and novel ion-beam-milling techniques. Ridge waveguides were formed by post-regrowth processing and heteroepitaxial ridge overgrowth. Distributed feedback ridge lasers were characterized by room temperature CW threshold currents as low as 40 mA, two facet external quantum efficiencies of up to 40 percent and stable transverse mode operation up to the output power of 10 mW. In strongly coupled devices, even with a cleaved resonator, the Bragg mode intensity exceeds that of the residual Fabry-Perot modes by a factor of 4000:1. Stable, single longitudinal mode operation was obtained under modulation rates as high as 4 GHz and error free transmission experiments over 60-km lengths of single mode fiber reproducibly performed at data rates as high as 2 Gbit/s. View full abstract»

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  • Spread spectrum fiber-optic local area network using optical processing

    Page(s): 547 - 554
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    Spread spectrum code division multiple access (CDMA) allows asynchronous multiple access to a local area network (LAN) with no waiting. The additional bandwidth required by spread spectrum can be accommodated by using a fiber-optic channel and incoherent optical signal processing. New CDMA sequences are designed specifically for optical processing. It is shown that increasing the number of chips per bit, by using optical processing, allows an increase in capacity of a CDMA LAN. An experiment is performed demonstrating the performance of an optical CDMA LAN, operating at 100 Mbd with three users. View full abstract»

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  • The influence of mode partition fluctuations in nearly single longitudinal mode lasers

    Page(s): 516 - 519
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    A simple relationship between the mode ratio of a two-mode laser and an empirical mode partition coefficient is derived. The effects of the mode ratio of a two-mode laser on the bit-error-rate floor of an optical fiber system are calculated, and the power penalties due to mode partitioning in the presence of Gaussian receiver noise are evaluated. The analysis provides a simple way to calculate the effects of mode ratio on the sensitivity of optical receivers. View full abstract»

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  • Effect of Rayleigh backscattering from optical fibers on DFB laser wavelength

    Page(s): 555 - 559
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    The effects of Rayleigh backscatter feedback from single-mode fibers on the spectral behavior of 1.5μm InGaAsP DFB lasers were measured. Rayleigh backscattering narrows the laser linewidth and induces frequency hops. The probability distribution for finding the laser at a particular frequency is reasonably approximated by a Gaussian distribution which has a width proportional to the laser-fiber coupling efficiency. Laser frequency excursions up to 1 GHz were observed and larger shifts are predicted to occur for stronger laser-fiber coupling. The experimental results agree well With a theory based on the Van der Pol oscillator model. View full abstract»

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  • Reduction of lasing threshold current density by the lowering of valence band effective mass

    Page(s): 504 - 506
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    In present day semiconductor lasers, there is a serious asymmetry between the very light conduction band mass and the very heavy valence band mass. Under laser threshold conditions, the hole occupation remains classical even while the electrons are degenerate. This results in a significant penalty in terms of threshold current density, carrier injection level, and excess Auger and other nonradiative recombination. We propose a combination of strain and quantum confinement to reduce the valence band effective mass and to lessen the laser threshold requirements. View full abstract»

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  • Two signal processing enhancements for optical time domain reflectometry

    Page(s): 538 - 546
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    Because time domain response of the backscattered signal in optical fibers is essentially exponential, there is 6-8 dB signal gain obtainable by using a logarithmic amplifier before any form of averaging, in the weak signal limit. Furthermore, the direct summation averaging of noisy traces (instead of the usual weighted averaging) is simpler because the required OTDR information is essentially relative. View full abstract»

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  • Passive components for multimode fiber-optic networks

    Page(s): 490 - 496
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    A new manufacturing technique is described by which all types of passive optical fiber components required in a network can be made. View full abstract»

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  • Pulse-shape effects on frequency chirping in single-frequency semiconductor lasers under current modulation

    Page(s): 497 - 503
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    Directly modulated semiconductor lasers exhibit dynamic frequency shifts (chirping) due to gain-induced variations of the refractive index. Using the small-signal analysis of the single-mode rate equations, the effect of current-pulse shape on frequency chirping is analyzed, and the results are compared for the cases of sinusoidal and square-wave modulations. The chirp is generally larger for the square-wave case. However, its magnitude depends on the pulse rise and fall times, decreasing for a pulse with slower turn-on and turn-off characteristics. Chirp analysis presented here includes the effect of power-dependent gain changes arising from the processes such as spectral hole-burning. 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