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Lightwave Technology, Journal of

Issue 4 • Date Apr 1993

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Displaying Results 1 - 18 of 18
  • Compensation for chromatic dispersion and nonlinear effect in high dispersive coherent optical repeater transmission system

    Page(s): 603 - 611
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (608 KB)  

    A design for a chromatic dispersion equalizer that provides 4.4 times higher efficiency in the dispersion compensation characteristics, compared with a conventional equalizer, is proposed. In addition, the amplitude response slope in the frequency domain is less than half of the conventional characteristic. This extends the compensation limit for chromatic dispersion up to 82500 ps/nm for a 2.5-Gb/s heterodyne system, which corresponds to a 4900-km normal dispersion fiber transmission system. A compensation method for modulational instability is also proposed. The method was confirmed by a 2.5-Gb/s continuous-phase frequency-shift-keying (CPFSK) 764-km normal dispersion fiber transmission experiment, with the abovementioned chromatic dispersion equalizer. Employing computer simulations, an over-1000-km normal dispersion fiber optical repeater transmission system with 2.5-Gb/s CPFSK heterodyne detection was shown to be feasible View full abstract»

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  • Design and performance of externally modulated 1.5-μm laser transmitter in the presence of chromatic dispersion

    Page(s): 624 - 632
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (732 KB)  

    Key laser and modulator characteristics that impact the use of externally modulated lasers in the presence of chromatic dispersion, excluding effects due to fiber nonlinearities, are reviewed. After a brief consideration of transmission performance with directly modulated 1.5-μm DFB lasers which have limited application of up to 80 km at 2.5 Gb/s, the key design characteristics of externally modulated transmitters are discussed. Experimental results showing the effects of modulator chirp and laser linewidth at a 2.5-Gb/s transmission rate are presented. It is found that lasers with CW linewidth under 100 MHz have less than 2-dB dispersion penalty for 600 km of non-dispersion-shifted fiber. Lower dispersion penalties can be realized if the modulator chirp is tuned so as to narrow the transmitted pulses. Excellent modulator stability is demonstrated for 60 days of error- and degradation-free 2.5-Gb/s operation View full abstract»

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  • Stability of the asymmetric nonlinear mode trapped in symmetric planar waveguides

    Page(s): 577 - 581
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (400 KB)  

    The authors examine the reliability of the numerical approach for studying the asymmetric nonlinear mode trapped in a thin linear film sandwiched in an infinite self-focusing medium, and thus resolve a controversy in the literature on the stability of the mode trapped between the bifurcation point and the transition point on the dispersion curve reported. They demonstrate that as a result of the instability there exists a class of quasi-periodic solutions arising from the instability in the asymmetric mode on the unstable branch and weakly stable branch. In addition, the effect of loss on the propagation characteristics of the nonlinear mode is investigated. The evolution is shown to follow the dispersion curve adiabatically in the stable region provided the loss is small, whereas the initial excitation on the unstable branch leads to evolution away from oscillation around the dispersion curve View full abstract»

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  • 10-Gb/s, 4-channel wavelength division multiplexing fiber transmission using semiconductor optical amplifier modules

    Page(s): 612 - 618
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (676 KB)  

    A dense wavelength-division-multiplexing (WDM) transmission system with very-high-speed channels was investigated experimentally. A 10-Gb/s four-channel WDM optical transmission (total capacity of 40 Gb/s) over a 40-km dispersion-shifted fiber was achieved by using hybrid-integrated DFB-LD/driver modules for transmitters and two cascaded semiconductor optical amplifier (SOA) modules for receivers. The experiment confirmed that the SOA is applicable for WDM transmission systems with high bit rates because of its inherent wide bandwidth. The transmission capacity of 40 Gb/s, achieved using an intensity modulation/direct detection (IM/DD) scheme, is the highest ever reported. This technology will make possible ultralarge capacity (up to several-hundred gigabits per second) and long-haul transmission systems in the future View full abstract»

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  • Real time control of arc fusion for optical fiber splicing

    Page(s): 548 - 553
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (464 KB)  

    A real-time control procedure has been developed for controlling arc fusion splicing of optical fibers. This procedure is applied during the fusion in order to optimize the fusion parameters for different types of optical fibers under different electrode conditions. The procedure has been implemented in a fusion splicer. Consistent splice losses have been achieved for different fibers under different fusion environment View full abstract»

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  • Analysis of wavelength-selective photodetectors based on grating-assisted forward coupling

    Page(s): 560 - 566
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (596 KB)  

    Grating-assisted vertical directional couplers can be combined with evanescently coupled absorption layers to realize integrated wavelength-selective photodetectors. The multimode structure of a photodetector including layered waveguides is studied, and mode transfer from the lossless filter section to the absorptive detector section is analyzed. By optimizing the device structure, the background absorption of unselected wavelengths can be suppressed, and, as a result, high crosstalk attenuation can be obtained. The filter bandwidth can be designed to cover a wide range from on the order of 10 nm down to the order of 0.5 nm with a device length that is shorter than 2 mm, which makes it suitable for various types of wavelength-division-multiplexing systems View full abstract»

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  • Polarization insensitive homodyne detection with all optical processing based on the photorefractive effect

    Page(s): 633 - 638
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (508 KB)  

    An optical homodyne PSK detection scheme based on the photorefractive effect in BaTiO3 has been investigated. The system uses polarization locking to implement a polarization insensitive receiver using all optical processing and only one detector. A theoretical analysis of the detection process is presented and verified experimentally. The system is shown to have a sensitivity of -52 dBm with S/N=2. The rate at which the system responds to changes in the incoming signal state of polarization is also investigated View full abstract»

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  • Two-layer waveguiding structure in LiNbO3 with birefringence reversal for refractive-index sensors with large measurement range

    Page(s): 554 - 559
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (512 KB)  

    A two-layer structure in LiNbO3 fabricated by Ti-indiffusion and proton exchange has been developed and studied. This structure is especially suitable for constructing refractive-index sensors with a large measurement range. Besides its high sensitivity this structure offers some additional advantages, including the possibility of optimizing the sensitivity for a given measurand and the elimination of the necessity for buffer layers. The largely different sensitivities of the fundamental TE0- and TM0-modes achieved allows the measurement and the reference channel to be incorporated in the same waveguide. This allows a new type of polarization interferometry that increases the flexibility of the refractive-index sensor design View full abstract»

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  • A new edge detector for CMI optical fiber transmission with improved jitter tolerance

    Page(s): 654 - 660
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (512 KB)  

    An edge detecting scheme for coded mark inversion (CMI) line codes which can reject wrong slot errors is proposed. This scheme looks at data transitions over one-and-a-half symbol durations and makes a binary decision based on the most likely transition pattern. An analysis and measurement results for the bit-error-rate performance of this scheme over an optical fiber link which show improvements in the detector tolerance against symbol timing jitters are presented View full abstract»

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  • Four channel integrated DFB laser array with tunable wavelength spacing and 40-Gb/s signal transmission capacity

    Page(s): 619 - 623
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (440 KB)  

    A four-channel distributed-feedback (DFB) laser array integrated with four heating filaments has been fabricated for high-density wavelength-division-multiplexing systems. The DFB lasers have a threshold current of 4 mA at room temperature. By changing the power in the heater, the wavelength of each laser can be continuously tuned by as much as 5 nm. Therefore, a tunable wavelength spacing anywhere from 1 nm to 2 nm can be achieved. Each laser can operate at 10 Gb/s. However, the bias current has to be increased to avoid the degradation of the eye pattern as the wavelength is thermally tuned over 2 nm. An electric crosstalk of 0.6 dB is measured when two adjacent lasers are modulated at 10 Gb/s simultaneously View full abstract»

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  • Frequency response and phase-shift nonlinearity of a cylindrical PVF2-film-based fiber-optic phase modulator

    Page(s): 595 - 602
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (696 KB)  

    A cylindrical coil configuration for a polyvinylidene-fluoride (PVF2)-film-based fiber-optic phase modulator is studied, focusing on the frequency response and the nonlinearity of the phase shift at the resonant frequency. This configuration, hitherto used for PVF2 film modulators, offers resonance at well-defined, controllable, and higher frequencies than possible for the flat-strip configuration. Two versions of this configuration that achieve selective mode suppression or enhancement and hence provide a choice of the resonance frequency at which a large phase shift occurs are presented. It is shown that a coil version in which the fiber loops are bonded strongly to each other leads to large reduction in the phase shift. A comparative study of the existing piezoelectric fiber-optic phase modulator designs is also presented View full abstract»

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  • Wide angle phase-corrected Y-junction of dielectric waveguides for low loss applications

    Page(s): 567 - 576
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (872 KB)  

    An approach to designing very-low-loss, wide-angle Y-junctions for dielectric waveguides is proposed. By introducing two interface planes with properly chosen parameters in the branching region, the conditions for a close (phase) match between the incident field and a desired output distribution suitable for minimal junction scattering are realized. An accurate and numerically efficient method for analysis and design of the proposed structure is described. Numerical results for some sample designs along with a set of simple design criteria are discussed View full abstract»

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  • Optimal transmission condition of nonlinear optical pulses in single-mode fibers

    Page(s): 542 - 547
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (364 KB)  

    Optimal conditions for transmission of nonlinear optical pulses in single-mode fibers are presented. When an optical pulse propagates in a fiber, it suffers fiber loss, group velocity dispersion, and self-phase modulation. An optimal output pulse can be obtained by choosing a suitable optical carrier wavelength and an initial input pulse. The system under optimal conditions not only has a more stable performance than the dispersion-free system, but also achieves maximum transmission bit rate for a fixed transmission distance. A bit-length product up to 8550 Gb/s-km or more can be achieved by using dispersion-shifted fibers without amplification View full abstract»

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  • Structural influence of proton exchange on domain-inverted lithium niobate revealed by means of selective etching

    Page(s): 589 - 594
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (592 KB)  

    Selective etching is used to study the influence of different proton-exchange methods on the crystal structure of periodically domain-inverted lithium niobate. The annealed proton-exchange method is shown to interfere strongly with previously patterned domains. A less common graded proton-exchange method that leaves the ferroelectric domain structure intact is demonstrated View full abstract»

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  • Effect of laser phase noise in Sagnac interferometers

    Page(s): 643 - 653
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    A theoretical analysis of the responsivity and the noise caused by backscattering in a Sagnac interferometer used as a sensor for reciprocal measurands, such as acoustic waves, is presented. Both Rayleigh backscattering and reflections from splices are taken into account. The noise power is found to increase proportionally to the source coherence time, and a noise equivalent phase shift in the range of 0.1×10-6 rad r.m.s./Hz1/2 is predicted for typical fibers and diode lasers. Experimentally, a noise equivalent phase shift of 2.5×10-7 rad r.m.s./Hz1/2 at 10 kHz was observed, with a detector current of 3 μA View full abstract»

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  • Failure analysis of connector-terminated optical fibers: two case studies

    Page(s): 537 - 541
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (832 KB)  

    Two of the most common fiber-optic connector failures involve fiber breaks caused by thermal changes. Type I failures involve fiber buckling during cooling from the epoxy cure temperature and are related to the free length of fiber inside the ferrule/backbone assembly. Type II failures occur during the heating phase of thermal cycling and are caused by expansion of epoxy in the ferrule entry under certain conditions. These conditions lead to otherwise unexpected tension at the ferrule capillary entry. In both cases the failure probability is increased by fiber damage during the termination process. Examples of the two types of failure are presented together with a discussion of the mechanisms and the reliability implications View full abstract»

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  • Spot size expansion for laser-to-fiber coupling using an integrated multimode coupler

    Page(s): 582 - 588
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (724 KB)  

    Efficient coupling of light from a semiconductor waveguide to an optical fiber is difficult to achieve due to the inherent differences in the spot sizes. The problem is particularly severe in the vertical dimension. The use of a uniform, untapered, intermediate coupler structure which consists of a multimode waveguide is proposed. This structure has potential for integrating with the semiconductor waveguide. The basic design rules for this coupler are worked out using coupled-mode theory, and the detailed designs are based on direct calculation of the mode profiles in the coupler. A range of realistic examples is examined, and it is shown that the butt coupling efficiency from a typical semiconductor laser to an optical fiber can be improved by up to 5 dB. The dependence of performance on fabrication tolerances is also studied View full abstract»

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  • Linearly configured embedded fiber-optic acoustic sensor

    Page(s): 639 - 642
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (296 KB)  

    A linearly configured fiber-optic acoustic sensor has been developed by embedding a single-mode fiber in a polyurethane cylindrical layer. The acoustic sensitivity was studied in the range of 0.75-10 KHz and was found to be frequency independent and significantly higher than that of a free suspended fiber or a solid mandrel fiber sensor. A comparison is mace between this sensor and air-backed fiber-optic mandrel sensors 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