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Lightwave Technology, Journal of

Issue 9 • Date Sep 1989

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Displaying Results 1 - 18 of 18
  • Asymmetric channel gain and crosstalk in traveling wave optical amplifiers

    Page(s): 1351 - 1359
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (564 KB)  

    Previous studies have shown that in multichannel optical amplification using a traveling wave amplifier, nonlinear frequency mixing effects can arise due to the modulation of the carrier density. It was shown that in the small-signal case, the carrier density modulation leads to a weak asymmetry in the gains experienced by individual channels. The authors extend the theoretical results by including the effects of gain saturation. They find, in the two-channel case, that the gain asymmetry can be as large as 10 dB depending on the channel separation, carrier lifetime, and input powers. The authors discuss the implications of this on the choice of modulation scheme View full abstract»

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  • Timing jitter in semiconductor lasers under pseudorandom word modulation

    Page(s): 1394 - 1399
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (424 KB)  

    Timing jitter of semiconductor lasers under pseudorandom word modulation was studied at 1 Gb/s. For lasers biased above threshold the timing jitter was Gaussian in distribution, with a turn-on timing jitter amplitude τ=2σ=±6 ps. For lasers biased below threshold, the turn-on timing jitter showed two peaks of Gaussian distribution, with an amplitude τ=60±10 ps and separated by about 80 ps. This phenomenon is due to a pattern-dependent effect of the laser turn-on delay. Theoretical calculations show that for data transmission above 2.2 Gb/s, the laser has to be biased above threshold to avoid excessive (>0.5 dB) jitter-induced power penalty View full abstract»

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  • Bit error rate performance for optical fiber systems with modal noise

    Page(s): 1285 - 1289
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (376 KB)  

    A gamma distribution is used to model the received optical power fluctuation in a digital fiber-optic system affected by modal noise. New recursive formulas for the moments of the receiver output current are obtained which can be used in the Gauss quadrature rule (GQR) approximation of the error probability integral. Error rates have been calculated for varying degrees of modal noise disturbance View full abstract»

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  • Strength and fatigue of silica optical fibers

    Page(s): 1360 - 1370
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (896 KB)  

    After a brief review of early lightguide work, the authors assess advances since the mid-1970s. They note important work on strength distributions and procedures for improving strength. This is followed by a discussion of long-length strength, prooftesting and splicing. Flaw character is studied along with strength degradation, fatigue limits, aging and fatigue, and hermetic coatings View full abstract»

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  • Light beam redistribution using computer-generated phase plates

    Page(s): 1412 - 1418
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (580 KB)  

    The use of two phase plates for light-beam power redistribution is proposed. The first plate is designed so that the desired power distribution is obtained by near-field diffraction; the purpose of the second plate is the correction of the phase front. The deviation is based on ray optics, which is a good approximation in practical situations. As an example, design and fabrication of the phase plate for 1:2 branching of single-mode fibers are described. The phase plates have a computer-generated pattern and are fabricated by electron-beam lithography. Experimental verification of beam branching is presented View full abstract»

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  • Compound Bragg reflection filters made by spatial frequency doubling lithography

    Page(s): 1379 - 1385
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    A report is presented on the fabrication of complex Bragg filters with resonant wavelengths near 1.55 μm, patterned by photolithography using a high-resolution deep ultraviolet stepper. The projection of gratings with quarter-micrometer features was made possible by the use of spatial frequency-doubling lithography. A single chip, processed entirely in the silicon facility, was used to demonstrate five Bragg reflectors of different wavelengths, a quarter-wave shifted resonator, broadband stacked filters with as many as 15 uniform Bragg reflector sections of different Bragg wavelengths, and broadband stacked filters containing a passband within the reflection band. The filters exhibited nearly ideal spectral behavior View full abstract»

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  • Crosstalk in a two channel coherent fiber optic FSK system using a semiconductor laser amplifier

    Page(s): 1319 - 1322
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (312 KB)  

    Bit-error-rate measurements on a two-channel optical transmission system using a low-reflectivity laser amplifier are presented. The signal lasers are directly frequency-modulated or amplitude-modulated at 1 Gb/s. The crosstalk penalties in an FSK-FSK system are very small and are mainly attributed to the residual small amplitude modulation of the lasers resulting from the direct frequency modulation. The crosstalk in an ASK-FSK system is considerably larger View full abstract»

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  • Frequency correlation function of modal noise in multimode optical fibers

    Page(s): 1300 - 1307
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (508 KB)  

    After transmission of highly coherent light through a multimode optical fiber, it is possible to observe a speckle pattern, namely, a modal noise, at its exit face caused by the interference of many different propagation modes. Changes of the source frequency can also cause modal noise variations in time at the exit face. The statistics of the modal noise appearing at the exit face of a fiber can thus be used to study the properties of the fiber and source. Measurements have been made of the frequency correlation function of modal noise in multimode optical fiber not only at the exit face of the fiber but also at a nearby point. A geometrical approximation is used to derive the frequency correlation function at the detecting position for various detecting positions. Experimental results are given and compared with the theory View full abstract»

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  • Spatial frequency doubling lithography (SFDL) of periodic structures for integrated optical circuit technology

    Page(s): 1386 - 1393
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (804 KB)  

    A novel technique for fabricating gratings useful for integrated optical circuits (IOCs) is described. The technique combines optical projection lithography, partially coherent illumination, and spatial filtering. With this technique, only the first two orders diffracted by the mask grating are allowed to pass through the lens. This produces a grating pattern in the image plane that has a high contrast (near 100%), a large depth of focus, and a period half of what would have been obtained in normal imaging. Gratings of different periods, sizes, locations, orientations, and configurations (chirped, phase-shifted, etc.) can all be produced on the same chip with a single exposure. Using a deep UV lens with 248-nm KrF excimer laser for illumination, the authors printed high-quality 0.5-μm period gratings in an oxide layer on 10 mm×10 mm silicon chips. Extended depth of focus was observed. This technique opens up the possibility of high-volume production of IOC chips with Bragg filters using standard IC fabrication facilities View full abstract»

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  • Crosstalk in fiber Raman amplification for WDM systems

    Page(s): 1407 - 1411
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (396 KB)  

    The crosstalk between channels in Raman amplification for two-channel WDM system is calculated. Theory shows that severe crosstalk can occur even in the linear amplification (or pump undepletion) region. To ensure small crosstalk, the signal gain and injected pump power should be limited to values well below the threshold of Raman amplification. As a numerical example, a 30-dB gain penalty and 3-dB pump power penalty occur when a 30-dB signal-to-interference ratio (SIR) is required. Thus, the conversion efficiency of Raman amplification in WDM systems is very low View full abstract»

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  • Analysis and observation of coupling ratio dependence of Rayleigh backscattering noise in a fiber optic gyroscope

    Page(s): 1323 - 1328
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (500 KB)  

    Noise due to Rayleigh backscattering in a fiber-optic gyroscope is observed in quadrature with the Sagnac signal. This noise can be nulled by adjustment of the coupling ratio of the loop coupler and the state of polarization in the gyro loop. A rigorous analysis of the phases of, and the modulations applied to, the primary and scattered beams shows that no coherent Rayleigh backscatter noise should be detected on the Sagnac signal even with relatively coherent semiconductor laser sources View full abstract»

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  • Subcarrier multiplexed lightwave systems for broad-band distribution

    Page(s): 1329 - 1342
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1152 KB)  

    Microwave subcarrier multiplexing (SCM) is an important approach to the design of lightwave systems for broadband distribution. Recent progress in the design and performance of both analog and digital multichannel SCM systems is reviewed. The application of broadband SCM systems to both passive and optically amplified distribution networks is discussed. The discussion covers the general features of SCM systems; the electrooptic components that have been used in the system experiments described here, including laser intensity noise and noise due to intermodulation products; the carrier-to-noise ratio requirements; some multichannel FM systems experiments; and a 20-channel digital systems experiment; and a hybrid system carrying 60 FM SCM channels plus a 100-Mb/s baseband digital channel. Several approaches to broadband subscriber distribution networks are analyzed View full abstract»

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  • Coupled waves on optical fibers by power conservation

    Page(s): 1400 - 1406
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (604 KB)  

    Using only power conservation, the authors derive the coupling coefficients of coupled-mode theory and a new power conservation law. The derivation provides physical insight into the mechanism of wave coupling on optical fibers. It shows explicitly that the coupled-mode approximation is not generally applicable to Maxwell's equations, since the polarizability of perturbations is omitted. Examples include nonlinear fiber couplers and fiber nonuniformities, with emphasis on their polarization characteristics. An important class of unsolved problems is revealed View full abstract»

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  • Signal light amplification by stimulated Raman scattering in an N-channel WDM optical fiber communication system

    Page(s): 1290 - 1299
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (668 KB)  

    The use of forward and backward Raman amplification in an N -channel wavelength-division-multiplexing (WDM) optical-fiber communication system is analyzed. Analytical expressions for the signals, the pumps, and the amplified spontaneous scattered power (ASSP) are presented. The crosstalk among the signal channels is analyzed in terms of system parameters. It is found that the crosstalk is negligible while low pump power is used and becomes significant if high pump power is used. The signal-to-ASSP ratio can be improved by increasing pump power; however, the improvement is small when pump power is already high. A 300-km repeater spacing with more than 20-dB signal-to-ASSP ratio is calculated View full abstract»

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  • A novel resonance-type optical receiver for high-speed optical heterodyne transmission systems

    Page(s): 1371 - 1378
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (624 KB)  

    A wideband resonance-type optical receiver (WROR) is proposed. It is based on inserting inductance in the feedback path of transistors to improve the frequency bandwidth and noise characteristics of the ROR in the high-frequency range. The noise characteristics of conventional and resonance-type optical receivers are evaluated by considering the series resistance of photodiodes. The double-balanced wideband resonance-type optical receiver is also evaluated. Its frequency bandwidth is 5-12 GHz. Finally, a 5-Gb/s optical CPFSK modulation and demodulation experiment is carried out using this optical receiver View full abstract»

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  • Fiber-optic strain gauge

    Page(s): 1308 - 1318
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (856 KB)  

    Prototype fiber-optic strain gauges consisting of plastic fibers containing permanent microbends were fabricated and various properties were measured. Their strain sensitivity as a function of microbend amplitude is shown, and their transduction mechanism, which is primarily the drop in microbend amplitude under tension and the corresponding increase in the fibers' optical transmission, is discussed View full abstract»

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  • Lateral mode analysis in semiconductor lasers using a cubic spline approximation of the refractive index profile

    Page(s): 1419 - 1424
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (352 KB)  

    A method employing a cubic spline approximation of the refractive index to solve the one-dimensional wave equation is presented. The average errors and computation times are compared with those obtained using a staircase method and an improvement of several orders of magnitude in accuracy with only a small increase in computation time for a given step size is shown. An iterative algorithm to determine the propagation constant is also presented View full abstract»

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  • Measurement of optical waveguide coupling coefficients using multiple waveguide systems

    Page(s): 1343 - 1350
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (564 KB)  

    A method for simply and accurately determining the coupling coefficient between integrated optical waveguides is presented. Measurement of only a few features of the output power distribution from a linear array of identical guides is required. The result is most accurate for long samples, but approximates the coupling coefficient to well within a few percent even for samples shorter than one two-guide coupling length. Since waveguides in the array would be fabricated in the same way, perhaps the same substrate, as the device structures of interest, the method ought to be a useful and convenient one for device designers 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