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Lightwave Technology, Journal of

Issue 5 • Date May 1990

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Displaying Results 1 - 25 of 26
  • Phase-noise-free coherent optical communication system utilizing differential polarization shift keying (DPolSK)

    Page(s): 691 - 698
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (636 KB)  

    An optical communication system utilizing differential polarization modulation, which is free from phase noise, is discussed. The system proved to be immune to essentially all phase jitter. Separate square operations for the x and y channels, followed by multiplication of the two-channel outputs, effectively removed phase jitter. The delay-and-multiply circuit was directly incorporated in the paths of the frequency shifter and the coupler to the local oscillator laser, minimizing the optical power loss View full abstract»

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  • Electrostatically driven fiber-optic micromechanical on/off switch and its application to subscriber transmission systems

    Page(s): 722 - 727
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    The structural design of the switch element is evaluated theoretically and experimentally, and an optimum combination of membrane length and insulator thickness is obtained. Based on the results, a 32-element electrostatically driven switch array is fabricated; its switching performance was found to be excellent. The switch array is applied to a subscriber transmission system using an abnormal subscriber end. A disturbance light from an abnormal subscriber end is successfully interrupted View full abstract»

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  • Four-channel wavelength division multiplexers and bandpass filters based on elliptical Bragg reflectors

    Page(s): 748 - 755
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    Four-channel multiplexers and four-wavelength bandpass filters based on elliptical Bragg reflectors (EBRs) are discussed. The channel spacing is 50 Å near 1.56 μm. The EBRs are narrowband elliptical mirrors that can refocus light from an input waveguide to any one of a number of output waveguides. Spectrally, they perform similarly to Bragg reflectors. The devices were fabricated on silicon using silica-based waveguide technology. The elliptical gratings with 0.53-μm periods were patterned using deep UV spatial frequency doubling photolithography. Multiplexers with single filtering and double filtering were demonstrated. With single filtering, the fiber-to-fiber insertion loss was 3.0±0.5 dB, and the crosstalk was -20 dB; with double filtering, the insertion loss was 4.0±0.5 dB, and the crosstalk was -30 dB. About 2 dB of this loss was due to coupling between the fibers and the waveguide. The additive loss associated with the EBR, including propagation, Bragg reflection, and coupling between input and output waveguides, was about 1 dB View full abstract»

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  • Analysis of a new microwave low-loss and velocity-matched III-V transmission line for traveling-wave electrooptic modulators

    Page(s): 728 - 738
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (832 KB)  

    A new microwave transmission line with low loss and velocity matched to a lightwave for a III-V traveling-wave electrooptic modulator has been analyzed using the spectral domain technique. A bandwidth of >40 GHz and a half-wave voltage Vπ of <6 V are predicted for the modulator View full abstract»

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  • A photonic wavelength-division switching system using tunable laser diode filters

    Page(s): 660 - 666
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    A photonic wavelength-division switching system using semiconductor tunable wavelength filters is proposed. A switching system using wavelength switches and multistage switching networks is discussed. A crucial point in developing this switching system is to achieve a large number of wavelength-division channels. The potential of 100 wavelength-division channels in such switching systems is estimated, based on InP optical integrated circuits. A wavelength network synchronization which permits the network to utilize such a large number of wavelength-division channels without wavelength misalignment and drift is proposed. An eight-channel wavelength-division switching experiment, using phase-shift-controlled distributed feedback laser diodes as tunable wavelength filters, is reported View full abstract»

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  • Analysis of buried-channel waveguides and couplers: scalar solution and polarization correction

    Page(s): 642 - 648
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (436 KB)  

    Buried-channel waveguides and couplers are analyzed by perturbations and variational methods under the scalar approximation. Propagation constants of the first- and higher-order modes are calculated. When far from cutoff, both methods give nearly identical results. Near cutoff, the variational method predicts the dispersion characteristics more accurately. The methods can be easily implemented on a PC to produce the dispersion characteristics as well as the field patterns. Correction to the scalar solutions that accounts for the polarization effects due to the refractive index discontinuity and the material birefringence is included in the analysis View full abstract»

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  • Threshold gain difference requirements for nearly single-longitudinal-mode lasers

    Page(s): 704 - 715
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    The probability of error for lightwave systems affected by mode partition fluctuations is related to laser parameters, laser bias and modulation currents, transmission bit rate, and encoding format (NRZ, RZ). A simulation-based solution of stochastic rate equations governing the laser dynamics is used to determine a probabilistic description of mode partitioning. The description is applicable to formula-based methods of evaluating the probability of error. A truncated-pulse-train Gauss-quadrature-rule method is used to accommodate many features unique to the problem of assessing the performance implications of mode partitioning. Extensive numerical results quantify, for several systems, the required threshold gain difference between the lasing mode and the dominant side mode. For example, for 2.4-Gb/s NRZ modulation, the threshold gain difference requirement increased from 3 cm-1 to 7 cm-1 as the bias current of the laser decreases from 1.1 to 0.9 times the threshold current View full abstract»

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  • Effect of reflections on the drift characteristics of a fiber-optic passive ring-resonator gyroscope

    Page(s): 811 - 816
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    The effects of reflections on the drift characteristics of a fiber-optic passive ring-resonator gyroscope are shown both theoretically and experimentally. It is shown that the reflected light generated at the fiber ends causes nonreciprocal deformations on the resonant characteristics of a fiber-optic ring resonator and results in a drift on the gyro output. However, a rotation-detection sensitivity as high as 3×10-5 rad/s (τ=30 s) was obtained by reducing the effects of the reflected light with an optical phase modulator View full abstract»

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  • Phase noise and polarization state insensitive optical coherent systems

    Page(s): 756 - 767
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    The authors present three different schemes that allow compensation of phase noise and polarisation state change by sending a reference channel that is suitably frequency shifted by using polarization modulation together with Stokes parameters detection or computing and inverting the Jones matrix that describes the fiber polarization state transformation. As a conclusion, some comparisons are made among different approaches in order to show how different systems can be tailored to different requirements both in point-to-point and in multipoint networks View full abstract»

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  • Stochastic instability in nonlinear anisotropic fiber couplers

    Page(s): 802 - 810
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (704 KB)  

    Transmission characteristics of a nonlinear coherent coupler composed of anisotropic fibers are investigated. The system mode approach and the channel normal mode approach are compared and shown to produce identical results so long as weakly guiding and weakly coupling structures are involved, as in the linear case. It is found that the critical state at which the power is equally divided into two channels at any long coupler lengths, as predicted in the early literature, does not exist in a conventional nonlinear coherent coupler unless the initial excitation beam is oriented along the coupler geometric axes. The existence of stochastic instability in a nonlinear anisotropic fiber coupler is shown even when the modes of the individual cores are excited. This result is different from the conclusion reported in the early literature with the assumption of negligible intensity-induced power exchange between the axes. The reason for such instability and the way to avoid it are also discussed View full abstract»

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  • New simplified method for designing the smooth-transition gradient-index and geodesic waveguide lenses of radial symmetry

    Page(s): 667 - 672
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (404 KB)  

    A concept of designing refractive-index and geodesic-description profiles for smooth-transition (non-full-aperture) waveguide lenses which is based on preliminary knowledge of the continuous deflection function is presented. Within the framework of this formulation the computations involved are significantly reduced in comparison with those resulting from a traditional description, and they provide exceptionally simple solutions, as proved by numerical examples View full abstract»

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  • Error analysis for refractive-index profile determination from near-field measurements

    Page(s): 625 - 633
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (612 KB)  

    Refractive-index profiles of diffused optical waveguides are determined by analyzing the near-field pattern of the waveguide. For this method, a computer simulation of measurement errors due to noise, quantization, defocusing, and nonlinearity of the camera system is presented by using data of a typical camera measurement system. The simulation procedure includes signal processing of the measurement intensity profile by means of a cubic spline approximation in order to reduce the influence of the measurement system errors. The residual errors associated with this technique are on the order of a few percent when measuring typical Ti:LiNbO3 waveguides View full abstract»

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  • Optical equalization to combat the effects of laser chirp and fiber dispersion

    Page(s): 649 - 659
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (884 KB)  

    Optical equalizers capable of combating the effects of laser chirp and fiber chromatic dispersion on high-speed long-haul fiber-optic communication links at 1.5 μm are described. They consist of both reflective and transmissive cavity structures. The equalizers are adaptive in the sense that the position of their periodic frequency responses are optimally adjusted in real time. The equalizers are evaluated by using computer simulation routines based on the rate equations for intensity-modulated lasers. It is shown that, by using equalizers of the type proposed, the receiver data eyes remain open well beyond where they would close without equalization View full abstract»

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  • An economic method for the solution of the scalar wave equation for arbitrary shaped optical waveguides

    Page(s): 789 - 793
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    The discrete sine method, in which the basis functions consist of sine functions defined on a set of parallel discretization lines, is discussed. The method is a combination of a scalar version of the finite difference method and sine method. The choice of the basis set leads for the eigenvalue equation to be solved, to a sparse matrix with a small bandwidth. As a consequence, the propagation constant of guided modes in optical waveguides may be calculated with short computation times and low storage needs. Results obtained with the method for three different wave guiding structures are compared with those of other methods View full abstract»

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  • A reduced capacitance concept for high-speed optical position-sensitive devices (PSDs)

    Page(s): 780 - 783
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    Position-sensitive devices (PSDs) in which the junction capacitance is reduced by using a mesh-type resistive layer with 125-μm pitch and 30-μm stripwidth are discussed. The temporal responses to pulsed excitation illuminated at the center are characterized by a rise time of less than 550 ns, which is shorter than that of the conventional type. The 14-mm×14-mm PSD has a junction capacitance of less than 180 pF, which is estimated to be lower than that of a conventional-type PSD by a factor of 2.4. By suitably selecting the mesh pitch and width, it is possible to reduce the temporal response by one or two orders of magnitude View full abstract»

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  • Improved transmission performance resulting from the reduced chirp of a semiconductor laser coupled to an external high-Q resonator

    Page(s): 716 - 721
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    The improvement in the receiver sensitivity due to the reduced chirp is examined for NRZ and RZ intensity modulation, direct detection systems operating in the 1.55-μm wavelength region with conventional single-mode optical fiber. The methodology involves (a) solving modified rate equations numerically for the optical power and phase of the external resonator laser in response to an injected current waveform, (b) modeling the signal transmission properties of single-mode optical fibers by convolution and modulus squared operations, and (c) using a truncated pulse train approximation to evaluate the probability of error in the presence of intersymbol interference, shot noise, avalanche photodiode multiplication noise, and preamplifier circuit noise. The numerical results indicate an almost threefold improvement in the achievable transmission distance for a bit rate of 4.8 Gb/s View full abstract»

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  • Bent planar waveguides and whispering gallery modes: a new method of analysis

    Page(s): 768 - 774
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    A matrix method for analyzing bent planar optical waveguides is discussed. The method is a modification of an earlier method which yields bend loss directly, inasmuch as a nonuniform refractive index is approximated by a series of linear profiles rather than a series of uniform profiles. The method can be used with absorbing or leaky structures. The effect of whispering gallery modes has also been studied. It appears that a whispering gallery explanation given by H.J. Harris and P.F. Castle (1986) may not be adequate View full abstract»

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  • Elusive bit-error-rate floors resulting from transient partitioning in 1.5-μm DFB lasers

    Page(s): 634 - 641
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    Some 1.5-μm distributed feedback (DFB) lasers modulated at 1.7 Gb/s exhibit bit-error rate (BER) floors for certain fiber lengths, and hence these floors are difficult to detect. For example, a laser that does not exhibit a BER floor for 43 km of fiber may exhibit a BER floor after only 27 km. It is shown that the source of such BER floors is a narrow pulse resulting from transient partitioning between the DFB TE and TM modes. The narrow TM pulses cause false bits if the fiber delay between the modes positions the TM energy within a zero time slot. It is shown that for the 11 lasers studied, TM partitioning floors rarely occur in lasers with adequate threshold gain difference. When the duration of the TM partitioning is only a small fraction of a bit period, the BER floor is effectively removed using a polarized film in the transmission path to suppress the TM mode. Similarly, increased suppression of the TM mode has been achieved by changing the laser structure to reduce the TM mode gain View full abstract»

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  • Bending loss evaluation of single-mode fibres with arbitrary core index profile by far-field pattern

    Page(s): 673 - 677
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (420 KB)  

    An evaluation of the bending loss of single-mode fibers based on the measured mode field is described. The field decay constant and the normalized field intensity in the cladding are determined. Experimental results verified the validity of this method. Its accuracy is determined by the accuracy of field measurement. The mode field is calculated from the far-field distribution measured with finite dynamic range of more than 50 dB. Far-field measurement with finite dynamic range limits the accuracy of field evaluation. Dispersion shifted fibers are easier for evaluation because of the wider far-field distribution. Bending loss and mode field diameter can be measured simultaneously, and the method is applicable to any single-mode fibers with a matched clad structure. A microbending loss formula is also determined by the decay constant and the normalized field intensity in the cladding as well as uniform bending loss View full abstract»

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  • Polarization-maintenance limits in polarization-maintaining fibers and measurements

    Page(s): 684 - 690
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    Intrinsic, extrinsic, and measurement-related polarization-maintenance transmission performance limitations are determined on short fiber lengths of hybrid-rectangular polarization-maintaining fibers and compared with previously reported limits. A direct polarization intensity extinction ratio -52.4±0.04 dB was obtained using automated measurement techniques. System measurement capability is limited by the lenses to -60 dB. Polarization-maintenance transmission limitations in the measurement polarizers and in cladding modes for short polarization-maintaining fibers were found to be negligible. New polarization-maintenance limits are presented to provide more precise measurement of the performance of short polarization-maintaining fibers View full abstract»

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  • Waveform degradation due to dispersion effects in an optical CPFSK system

    Page(s): 775 - 779
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (332 KB)  

    Waveform degradation due to polarization and chromatic dispersions in a single-mode fiber is calculated for a coherent CPFSK signal. For a single-mode fiber with polarization dispersion of ⩽1 ps, chromatic dispersion almost dominates the system. However, if a fiber has polarization dispersion of more than a few picoseconds and a chromatic dispersion of less than 0.1 ps/km/nm, which can be attained by using a dispersion-shifted fiber and/or by electric dispersion compensation, polarization dispersion will restrict transmission capacity. For instance, polarization dispersion of 5 ps will restrict a bit rate by ~60 Gb/s when chromatic dispersion is fully reduced using a dispersion-shifted fiber or applying electrical equalization View full abstract»

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  • Chirping-induced waveform distortion in 2.4-Gb/s lightwave transmission systems

    Page(s): 699 - 703
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (376 KB)  

    The performance of high-speed lightwave transmission systems operating in the 1.55-μm-wavelength region with conventional single-mode optical fiber can be influenced by the dynamic wavelength chirping exhibited by directly modulated semiconductor lasers. In a recent paper (1989), the authors presented the first detailed analysis of the bit error ratio performance of lightwave systems influenced by chirping-induced waveform distortion. Here, additional numerical results which address the performance implications of the waveform distortion by considering the dependence of the receiver sensitivity on the decision time and decision threshold, the eye pattern, and bit error rate ratio pattern are presented. It is shown that the response of the linear receiver filter can influence the dependence of the receiver sensitivity on the decision time View full abstract»

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  • Theoretical investigation of light coupling phenomena in wavelength-flattened couplers

    Page(s): 678 - 683
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    A study of light coupling phenomena in wavelength-flattened couplers by normal mode analysis is discussed. The effective index method and step approximation of the taper are used to analyze the mode coupling in the fused-taper region. It is shown that coupler parameters such as the dissimilarity of the two fibers, the degree of fusion, the minimum taper waist and the taper length should be optimized to get flat coupling characteristics. The optimum relationship among these coupler parameters is determined for fused-taper couplers employing standard telecommunication fibers View full abstract»

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  • Fabrication tolerance of Ti:LiNbO3 waveguides

    Page(s): 784 - 788
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (268 KB)  

    A simulation program based on the three-dimensional beam propagation method (BPM) is used to study the fabrication conditions of single-mode Ti:LiNbO3 waveguides. The calculated cutoff wavelengths are in good agreement with experimental data. The thickness of titanium needed to support the fundamental and first-order modes for three Ti strip widths (6, 7, and 8 μm) is calculated. The two-dimensional BPM is used to calculate the coupling length from the fabrication conditions. Results are consistent with measured data. The fabrication tolerances of the coupling length of directional couplers are also presented View full abstract»

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  • A low-voltage 8×8 Ti:LiNbO3 switch with a dilated-Benes architecture

    Page(s): 794 - 801
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    An 8×8 switch array with a dilated-Benes architecture that greatly relaxes the crosspoint extinction ratio requirements needed to achieve low overall switch array crosstalk is discussed. This, combined with the low uniform switching voltages (9.2+0.2 V) of the 48 directional coupler crosspoints, facilitates high-speed low-crosstalk operation. The crosspoints can be switched in about 1 ns. The switch array is fully packaged with permanently attached single-mode fiber pigtails. The high data transfer rate inherent in lithium niobate switches in general, combined with the low crosstalk and high switching speed of this switch array, is a good match to the requirements of time-multiplexing switching 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