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Lightwave Technology, Journal of

Issue 3 • Date March 1989

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Displaying Results 1 - 17 of 17
  • Polymeric optical waveguide switch using the thermooptic effect

    Page(s): 449 - 453
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (752 KB)  

    An all-polymeric optical waveguide switch which uses total internal reflection from a thermally induced index barrier is discussed. Very large effective index changes Delta N=2*10/sup -2/ were found in the polymeric waveguide. The temperature under the evaporated stripe heater was measured from the change in its resistance. The effective index change due to the temperature increase agrees well with values calculated from the deflection angles. The operation of the switch is, apart from a small waveguide dispersion effect, polarization-insensitive. Switching times of about 10 ms were measured. It should be possible to reduce them to a few milliseconds in optimized thermal designs and with regulated power dissipation in the heater.<> View full abstract»

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  • High electron mobility transistor lightwave receiver for broad-band optical transmission system applications

    Page(s): 454 - 458
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (522 KB)  

    The design and construction of a broadband transimpedance lightwave receiver which features packaged, commercially available high-electron-mobility transistors is described. The receiver was constructed on a standard teflon printed circuit board with packaged tailed 30- mu m-diameter germanium avalanche photodiode as photodetector. A sensitivity of -25.5 dBm for 10/sup -9/ bit error rate was achieved at 1.31 mu m with a 5-Gb/s nonreturn-to-zero pseudorandom sequence provided by a commercial data generator and 1:4 analog demultiplexing at the receiver output.<> View full abstract»

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  • Signal processing in an optical polarization diversity receiver for 560-Mbit/s ASK heterodyne detection

    Page(s): 459 - 464
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (600 KB)  

    Polarization diversity is an alternative technique for coherent receivers to prevent loss to signal due to variations in the states of polarization (SOP) of the received signal field. It is shown experimentally and theoretically that there is no significant power penalty difference between a receiver with optimally adjusted gains and receivers with linear envelope detection and square-law detection. Experimentally, two amplitude-shift keying (ASK) heterodyne polarization diversity receivers with envelope detectors were demonstrated at 560 Mb/s, one using linear rectifiers, the other using square-law rectifiers. In both cases, the receiver sensitivity of -35 dBm at BER=10/sup -9/ was degraded by less than 1 dB as the received signal SOP was varied, in agreement with theory.<> View full abstract»

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  • MPPM: a method for improving the band-utilization efficiency in optical PPM

    Page(s): 465 - 472
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (830 KB)  

    Multiple pulse position modulation (MPPM) is proposed as a modulation method to improve the band-utilization efficiency in optical pulse position modulation (PPM). Optical PPM gives higher transmission efficiency (bit/photon) in optical communications but degrades band-utilization efficiency. The proposed method reduces the required transmission bandwidth in optical PPM to about half with the same transmission efficiency, thus increasing band-utilization efficiency. While in conventional optical PPM, only one optical pulse is transmitted in every signal block, multiple pulses are transmitted using this method. Information is represented by different combinations of the positions of these pulses. The principle of bandwidth reduction applied, the transmission characteristics of the proposed method, and examples of improvement in band-utilization efficiency are also shown.<> View full abstract»

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  • Multiplication noise of wide-bandwidth InP/InGaAsP/InGaAs avalanche photodiodes

    Page(s): 473 - 478
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (660 KB)  

    Measurements of InP/InGaAsP/InGaAs separate absorption, grading, and multiplication avalanche photodiode multiplication indicate that at high gains the excess noise factors approach values predicted by the conventional continuum theory. However, at lower gains the noise is suppressed. This is probably an artifact of the very thin multiplication layers which have been used to increase the gain-bandwidth product. From the frequency response of the noise power, a gain-bandwidth product of 60 GHz, which is consistent with the value of 57 GHz obtained directly from bandwidth measurements, is deduced.<> View full abstract»

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  • Three ways to implement interfacial techniques: application to measurements of chromatic dispersion, birefringence, and nonlinear susceptibilities

    Page(s): 500 - 513
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1347 KB)  

    Depending on the spectal width of the source illuminating an interferometer, measurement procedures can utilize either the whole interferogram, or only the fringe envelope, or only the fringe quick oscillations. With an ultraband spectrum source, a simplified adaptation of the methods of Fourier transform spectroscopy yields the variations of the test-fiber propagation constant over the whole wavelength-interval of the source. Chromatic dispersion can then be computed from a single interferogram. With narrower spectrum sources, only the fringe envelopes are utilized and yield measurements of mode delay, with application to chromatic and polarization mode dispersion. In this case, however, interferograms at several wavelengths are necessary. With even narrower spectrum sources, the fringe quick oscillations provide measurements of phase shifts, related to changes in the mode propagation constant, when outside perturbations are applied to the test fiber. A direct method for measuring the third-order nonlinear susceptibilities is discussed. In this case the outside perturbation is an intense pump laser field.<> View full abstract»

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  • Multiplexing of nonlinear fiber-optic interferometric sensors

    Page(s): 514 - 519
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (631 KB)  

    The scheme is demonstrated with a three-sensor array consisting of magnetic-field, pressure, and displacement sensors exhibiting resolutions at 1 Hz of 20 mu Oe/ square root Hz (limited by ambient noise), 0.1 kPa/ square root Hz, and 30 nm/ square root Hz, respectively. Multiplexing is accomplished by dithering each transducer at a different frequency and using parallel phase-sensitive detectors (PSD) at the interferometer output to demultiplex the information. A single Mach-Zehnder interferometer driven by a single unmodulated laser was used. Factors affecting the performance of the multiplexing scheme, including interferometric demodulation technique, PSD performance, and nonlinear transduction mechanism, are discussed.<> View full abstract»

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  • Influence of laser phase on 400-Mbit/s coherent optical DPSK system

    Page(s): 520 - 524
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (484 KB)  

    The influence of laser phase noise on a 400-Mb/s optical DPSK (differential phase-shift keying) system is experimentally investigated with linewidths ranging from 1.2 MHz to 8 MHz. This range corresponds to linewidth to bit rate ratios epsilon of 0.33-2%. The system performance with these nonzero linewidths is evaluated against a negligible linewidth performance baseline. The sensitivity degradation at a bit error rate of 10/sup -9/ increases from 1.8 to 7 dB as epsilon is increased from 0.33-1%. When epsilon is increased beyond 1%, bit error rate floors higher than 10/sup -9/ develop. These findings agree well with the existing theories and allow the generalization of these results to other bit rates, as well as establishing practical criteria for lasers to be used in DPSK systems.<> View full abstract»

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  • A strain sensor using twisted optical fibers

    Page(s): 525 - 529
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (488 KB)  

    A sensor using twisted optical fibers to detect the strain distribution along the length of an object is discussed. This sensor is based on the optical loss due to fiber curvature. The distributed strain along the sensor axis is converted into distributed optical loss. The relation between the strain and optical loss is theoretically derived and experimentally confirmed for uniform tensile strain. The dependence of the sensor characteristics on sensor structure and fiber parameter are also shown. Measurement of the strain applied to fibers in an optical cable is also discussed.<> View full abstract»

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  • Profile inhomogeneity in multimode graded-index fibers

    Page(s): 530 - 532
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (249 KB)  

    Profile parameters (g) of several multimode graded-index fibers have been measured. It was found that g may vary azimuthally by +or-0.15 or more in fibers for which the average value is between 1.8 and 2.2.<> View full abstract»

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  • Modeling of Ti:LiNbO/sub 3/ waveguide devices. I. Directional couplers

    Page(s): 533 - 539
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (654 KB)  

    An efficient modelling method to simulate Ti-indiffused LiNbO/sub 3/ channel waveguide devices from their design and fabrication parameters is discussed. Procedures are: (1) derivation of the two-dimensional (2-D) refractive index profile; (2) transformation of the 2-D transverse refractive index profile to its one-dimensional (1-D) effective index profile; and (3) use of the 2-D beam propagation method to analyze the device performance. With slight consistent adjustments on Ti-induced refractive index changes, it is possible to calculate the performance of directional couplers in good agreement with experimental measurements. This modeling method can be used to predict performance of future devices.<> View full abstract»

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  • Comparison between strong coupling theory and experiment for three-arm directional couplers in Ti:LiNbO/sub 3/

    Page(s): 540 - 554
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    The derivation of scalar coupled mode theory for TEM waveguide arrays is examined. It is demonstrated that four previously published methods are identical at this level of approximation. The accuracy of the theory and its application to a slab-waveguide model of a three-arm coupler is considered. It is shown that the coupled mode equations require modification for slowly varying arrays. Analytic expressions for the matrix coefficients are presented, and it is demonstrated that device input-output transitions have significant effect on the response. The model is compared with experimental measurements of three-arm couplers fabricated in Ti:LiNbO/sub 3/, and excellent qualitative agreement is obtained.<> View full abstract»

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  • Dynamic characteristics of high speed p-substrate GaInAsP buried crescent lasers

    Page(s): 560 - 567
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    A detailed behavior of 1.3- mu m GaInAsP p-substrate buried-crescent lasers emitting maximum output powers of more than 30 mW/facet is discussed. A 3-dB modulation bandwidth of 11.5 GHz, and relative intensity noise level of approximately -145 dB/Hz were observed at 5 I/sub th/. The two-tone intermodulation distortion was more than 30 dB below the 9-GHz subcarriers for a current modulation index of approximately 40%.<> View full abstract»

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  • The effect of laser chirping on lightwave system performance

    Page(s): 568 - 573
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    Directly modulated semiconductor lasers exhibit a dynamic wavelength shift (chirping) arising from gain-induced variations of the laser refractive index. The effect of laser chirping on the performance of multi-Gb/s lightwave systems operating at a wavelength of 1550 nm is investigated. Models suitable for computer-aided analysis are used to describe the dynamic response of the laser and the propagation of chirped optical pulses through a step-index single-mode optical fibre. A truncated pulse train, Gauss quadrature rule method is used to evaluate the average bit error rate of the receiver. This permits pattern effects in the transmitted optical waveform due to the laser dynamics and nonlinear optical power transmission properties of optical fibers to be included in the system model. The influence that modulation and device parameters have on the receiver sensitivity is assessed.<> View full abstract»

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  • Optical fiber splice loss predictions from one-way OTDR measurements based on a probability model

    Page(s): 490 - 499
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    It is well known that one-way optical time-domain reflectometry (OTDR) measurement contains a false contribution to the splice loss due to statistical fluctuations in light scattering among fibers. Using a large amount of collected data over splice losses from field installations, a two-dimensional probability distribution function with the actual splice loss and the one-way measured OTDR discontinuity as variables was fitted to the data. The five parameters of the chosen probability distribution were determined numerically from the observed data. The probability of keeping the splice loss below a target value based on the observed one-way OTDR reading was calculated and can be displayed in a curve or a table of values. The agreement between theory and experimental values is satisfactory for standard match clad single-mode fibers measured at 1.3-μm wavelength View full abstract»

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  • Efficient N×N star couplers using Fourier optics

    Page(s): 479 - 489
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (696 KB)  

    A technique for constructing an efficient N×N star coupler with large N at optical frequencies is described. The coupler is realized in free space using two arrays, each connected to N single-mode fibers. The highest efficiencies are obtained using a planar arrangement of two linear arrays separated by a dielectric slab serving as free-space region. The coupler is suitable for mass production in integrated form, with efficiencies exceeding 35% View full abstract»

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  • Drawing influence on the lifetime of optical fibres

    Page(s): 555 - 559
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    Strength and lifetime measurements carried out on optical fibers with different residual tensile stress at the surface are discussed. This stress was optically measured and included in the theory of fiber strength and lifetime. The strength results were compared with measurements done on pure silica fibers without residual stress. In lifetime predictions, this residual tensile stress in the outside region of the fiber has to be taken into account. However, the decrease in intrinsic strength was much larger than the increase in residual stress in the outside region of the fiber. This phenomenon, which is not well understood, depends on drawing conditions 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