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Lightwave Technology, Journal of

Issue 4 • Date Apr 1995

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Displaying Results 1 - 19 of 19
  • Laser turn-on delay and chirp noise effects in Gb/s intensity-modulated direct-detection systems

    Page(s): 666 - 674
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (836 KB)  

    This paper describes a new IM/DD optical transmission system simulation which incorporates the impact of laser diode stochastic turn-on effects on system performance. Using this simulation, experimentally observed error rate floors, due to inappropriate laser diode biasing, can be theoretically modelled and predicted, for the first time View full abstract»

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  • Simultaneous measurement of the linewidth, linewidth enhancement factor α, and FM and AM response of a semiconductor laser

    Page(s): 592 - 597
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (436 KB)  

    Using a commercially available computer controlled spectrum analyser with tracking generator, optical input section, and optical delay line it is possible to measure the linewidth, linewidth enhancement factor α, and FM and AM response of a semiconductor laser in one process. The determination of the linewidth yields also information about the frequency noise density and the determination of a delivers information about the nonlinear gain. Assuming an optical input power of 0 dBm, a laser linewidth <50 MHz and a modulation response of the laser without cut-off, AM indices m>0.01% and FM deviations of about >10 MHz up to 20 GHz can be detected View full abstract»

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  • A method to determine the above-threshold stability of distributed feedback semiconductor laser diodes

    Page(s): 563 - 568
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (452 KB)  

    An analysis of the above-threshold stability of distributed feedback (DFB) semiconductor laser diodes (LD's) is presented. It is based on a numerical model which takes into account effects of spatial hole burning (SHB) and the nonlinear gain coefficient. In the analysis, the Newton-Raphson (NR) technique has not been used, and no functional derivative is required. Taking into account the presence of another nonlasing mode, the single-mode stability of the DFB laser diodes is determined. The proposed model does not depend on any particular DFB structure, and hence can be applied to various DFB LD structures. Numerical results are presented for a three-phase-shift (3PS) DFB LD View full abstract»

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  • Influence of imbalance on distortion in optical push-pull frontends

    Page(s): 650 - 657
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (640 KB)  

    The influence of imbalance on second-order intermodulation distortion (IMD2) in optical push-pull frontends for subcarrier multiplex CATV applications is investigated theoretically and experimentally. The investigation focuses on imbalance introduced in either the photodiode, the push-pull amplifier, or the output balun, and expressions describing the overall IMD2 cancellation efficiency are derived. The developed theory is used to predict the IMD2 cancellation behavior of an optical push-pull frontend. Commercially available PIN photodiodes for CATV purposes and ferrite core transformers are characterised for phase and amplitude balance up to 1 GHz. The overall IMD2 cancellation efficiency of an optical push-pull frontend based on the best of these devices is calculated. The theory is finally verified experimentally with an optical push-pull frontend designed with the characterised photodiode and transformer. The improvement in IMD2 suppression obtained with the push-pull structure relative to a single-ended structure is in average 29 dB across the band from 47-862 MHz. The total IMD2 suppression obtained for the frontend is between 60 dBc and 79 dBc at an average optical input power of 1 mW and with an optical modulation index (OMI) of 35 percent per carrier in a two-tone setup, View full abstract»

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  • Rigorous analysis of form birefringence of weakly fused fiber-optic couplers

    Page(s): 687 - 691
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (376 KB)  

    Based on a rigorous vectorial formulation, the surface integral equation method is used to solve the vectorial mode patterns and the coupling characteristics of weakly fused fiber-optic couplers. Form birefringence versus aspect ratio of the coupler cross-section for different normalized frequencies V are calculated. A dramatic feature-that there is a local maximum of form birefringence for the weakly fused couplers with large V-values-is found. The dependence of the aspect ratio at which the coupler is isotropic on the V-value is also presented. The fused coupler with large V-value is isotropic as the aspect ratio is close to 1.8, but its polarization effect is still significant when the aspect ratio is 2.0 View full abstract»

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  • Effect of laser-diode power change on optical heterodyne interferometry

    Page(s): 675 - 681
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (556 KB)  

    A dynamic interferometer with a frequency-ramped laser diode (LD) has been constructed that is based on an optical heterodyne technique. Effect of LD power change on the optical heterodyne interferometry has been investigated theoretically and experimentally. A general formulation of the interferometry has been presented in which the demodulation scheme is analyzed in the frequency domain by Fourier-transforming a beat signal. Phase errors caused by the LD-power variation alter sinusoidally with the same period as the interference beat signal. The error can be eliminated by using an amplitude-stabilized, frequency-modulated laser diode source in the interferometer. The stabilization of the LD amplitude can be achieved by a feedback system with a superluminescent diode as an external light-power controller View full abstract»

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  • Performance of linecoded optical heterodyne FSK systems with nonuniform laser FM response

    Page(s): 628 - 638
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (772 KB)  

    A simple theoretical analysis for evaluating the performance of linecoded optical frequency shift keying (FSK) systems is presented. It accounts for the combined effects of laser phase noise, receiver noise, and nonuniform BM response of distributed feedback lasers. A close form expression for the random frequency noise due to the combined effect of laser nonuniform FM response and phase noise is developed. The analysis is carried out for three different linecoding schemes, i.e., alternate mark inversion, Miller code or delay modulation, and Manchester coding, to investigate the efficacy of the line coding schemes in counteracting the effect of nonflat FM response. Theoretical and simulation results show that the sensitivities of linecoded FSK systems are within 0.7 and 0.4 dB for single-branch and dual-branch detection, respectively, at a bit error probability of 10-9 relative to the random non-return to zero FSK with flat FM response View full abstract»

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  • Gain optimization in switches based on semiconductor optical amplifiers

    Page(s): 598 - 605
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (616 KB)  

    The distribution of unsaturated gains that minimizes the noise figure of a three-stage optical switch based on semiconductor-optical-amplifier (SOA) gates is found. Gain saturation under both unidirectional (isolators inserted) and bidirectional (no isolators) propagation of spontaneous emission noise is analyzed, and a noise figure penalty associated with the absence of isolators is determined. Determination of the optimal set of pump currents is a nonlinear optimization problem, while determination of the optimum set of saturated gains is a linear optimization problem. The latter solution is found analytically, while the former solution requires a nonlinear optimization approach. The results are extended to the case of a sequence of N SOA's View full abstract»

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  • Stable soliton transmission in the system with nonlinear gain

    Page(s): 658 - 665
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (636 KB)  

    It is shown that the linear-wave growth in bandwidth-limited-amplified soliton transmission can be suppressed by a selective amplification of solitons by means of nonlinear gain that can be realized by using fast saturable absorbers. Numerical simulations assuming the use of nonlinear amplifying loop mirrors (NALM's) as the nonlinear-gain element show that 20 Gb/s soliton trains can be transmitted over transoceanic distances, Wavelength-division multiplexing is also feasible if demulti/multiplexers are used just before and after the NALM View full abstract»

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  • Enhanced wavelength tunability in asymmetric gain-levered quantum-well semiconductor lasers

    Page(s): 588 - 591
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (380 KB)  

    The wavelength tuning characteristics of two-section gain-levered Fabry-Perot quantum well laser diodes with unequal (asymmetric) facet reflectivities are investigated theoretically, taking into account the longitudinal variations of carrier and photon densities. It is demonstrated that, under appropriate biasing conditions, enhancement of wavelength tunability can be achieved in asymmetric Fabry-Perot laser diodes View full abstract»

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  • A joint finite-difference and FFT full vectorial beam propagation scheme

    Page(s): 692 - 700
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (656 KB)  

    A full vectorial beam propagation scheme is developed and it is applied on 3-dimensional waveguide structures. The formulation is based on the coupled wave equations for the transverse electric field. Each propagation step is performed by utilizing both the FFT and a finite-difference implementation. Under this perspective the offered advantages of FFT and finite-differences are exploited within a single propagation step resulting in a joint propagation scheme. The scheme is applied on a step-index circular fiber where analytical solutions are readily available for cross-checking. Moreover, the dependence of the phase constant on the reference refractive index is discussed. The polarized modes and the effective mode indices are derived in the case of rib waveguides by performing propagation along imaginary distance. Further, the rib waveguide coupler is examined and the energy transfer is simulated View full abstract»

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  • Comparison of fiber-optic Sagnac and Mach-Zehnder interferometers with respect to thermal processes in the fiber

    Page(s): 682 - 686
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (404 KB)  

    The impact of thermal noise in the fiber on the noise power and signal-to-noise ratio (SNR) of fiber-optic sensors is investigated, and sensors based on the Sagnac and the Mach-Zehnder interferometers are compared. The SNR is almost the same for the two interferometers; the Mach-Zehnder interferometer has slightly higher SNR at low frequencies, whereas the Sagnac interferometer may have a few dB higher SNR at high frequencies. It is also shown that thermal noise may dominate over shot noise for realistic system parameters, in which case a Sagnac interferometer has several advantages over a Mach-Zehnder interferometer View full abstract»

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  • Timing jitter due to carrier linewidth of laser-diode pulse sources in ultra-high speed soliton transmission

    Page(s): 639 - 649
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (880 KB)  

    We theoretically analyze the timing jitter due to both the carrier phase noise of laser-diode (LD) pulse sources and the Gordon-Haus effect in soliton transmission. A formula is derived for the timing jitter in terms of the carrier linewidth, one of the measurable parameters common to all types of LD pulse sources. The transmission distance restricted by the timing jitter is analyzed, and the carrier linewidths required for ultra-long distance and ultra-high speed soliton transmission are estimated as well. Recirculating loop experiments at 10 Gb/s are demonstrated using two pulse sources; a gain-switched DFB-LD and a sinusoidally driven monolithically integrated MQW-DFB-LD/MQW-EA modulator, which have different carrier linewidths due to their different pulse formation processes. The difference in the carrier linewidths of the two pulse sources is measured by the proposed technique which is based on the optical heterodyne method. The observed difference between the two pulse sources in terms of timing jitter accumulation and timing jitter reduction with optical bandpass filters for the two pulse sources well support the theoretical predictions View full abstract»

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  • Tunable coherent optical transversal EDFA gain equalization

    Page(s): 581 - 587
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (628 KB)  

    In this paper, we propose a fiber amplifier gain equalizer using a coherent optical transversal filter. The gain equalizer is tunable and has a bandwidth in the order of 30 nm. We also study the effects of different parameters such as input signal power pattern and the input pump power on the gain profile of the amplifier. The results show that, when the input signal power pattern changes, the amplifier does not maintain its gain profile. The gain profile has to be maintained in order to make the gain equalization effective. We show that, the pump input power can be adjusted so that the changes in the gain profile are compensated for. The gain profile varies quite slowly, hence compensation is feasible. As an example, we discuss the design of a gain equalizer for a system consisting of seven wavelength channels View full abstract»

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  • Field effect transistor-self electrooptic effect device (FET-SEED) differential transimpedance amplifiers for two-dimensional optical data links

    Page(s): 606 - 614
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (900 KB)  

    A 4×18 two-dimensional array of GaAs FET-SEED (field effect transistor-self electrooptic effect device) differential transimpedence receivers has been fabricated for application in massively parallel optical data link board-to-board interconnections. Several FET-SEED receiver arrays were tested and displayed a mean response of ~0.7 mV/μW, and were capable of >100 Mbps per channel operation. The mean receiver sensitivity for a BER of <10-9 was calculated from the measured noise spectrum to be -26.8 dBm at the system design rate of 40 Mbps (18 k-22 MHz bandwidth), and -23.2 dBm for a 100 Mbps rate (dc-66 MHz bandwidth). A sensitivity of approximately -25 dBm for the 40 Mbps rate was confirmed using a bit-error-rate test set. The theoretical noise is compared to measured values with good agreement assuming a FET channel noise factor of 1.4. The 1/f noise corner frequency of ~13 MHz was found to cause a ~1.2 dB degradation in sensitivity for the 100 Mbps rate. The differential amplifier mean dc output offset voltage was measured to be 10 mV, and displayed a large sigma due to parameter variations in the active devices. Two receiver arrays were successfully used in a demonstration of a fully differential parallel optical small computer system interface (SCSI) data link View full abstract»

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  • Self-consistent calculation of lasing modes in a planar microcavity

    Page(s): 575 - 580
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (568 KB)  

    The self-consistent calculation of lasing modes in a microcavity with infinite plane mirrors is presented. The semiclassical theory is used, with rigorous boundary conditions included for Maxwell's equations to describe both the emitter distribution and the cavity reflectors. The concept of gain-guided versus index-guided modes in such structures can be removed within the semiclassical model, as rigorous boundary conditions for both the radiation source and passive cavity can be handled exactly. We present calculated curves showing the angular dependence of various lasing modes on mirror reflectivity and the threshold gain susceptibility dependence on mirror reflectivity and active diameter. The linewidth dependence on the transverse lasing mode is also considered. Limitations of the semiclassical approach as compared to a fully quantum mechanical approach is emphasized View full abstract»

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  • Application of the spectral index method to laser diode design

    Page(s): 569 - 574
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (492 KB)  

    The spectral index method (SIM) is compared to the effective index method (EIM) and the beam propagation method (BPM) for the calculation of the optical mode index and mode profile in a prototypical distributed feedback (DFB) rib waveguide laser diode. Modal index is shown to be insufficient as a metric of comparison, so in addition to nmode , the quantum well filling factor Γ and grating coupling coefficient κ are included in the metric for comparison. SIM is found to yield superior results to EIM and to give results comparable to BPM almost two orders of magnitude faster View full abstract»

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  • Optical multi-mode interference devices based on self-imaging: principles and applications

    Page(s): 615 - 627
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1296 KB)  

    This paper presents an overview of integrated optics routing and coupling devices based on multimode interference. The underlying self-imaging principle in multimode waveguides is described using a guided mode propagation analysis. Special issues concerning the design and operation of multimode interference devices are discussed, followed by a survey of reported applications. It is shown that multimode interference couplers offer superior performance, excellent tolerance to polarization and wavelength variations, and relaxed fabrication requirements when compared to alternatives such as directional couplers, adiabatic X- or Y-junctions, and diffractive star couplers View full abstract»

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  • Bending loss reduction in silica-based waveguides by using lateral offsets

    Page(s): 555 - 562
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (596 KB)  

    The excess loss that occurs in waveguide bends can be minimized by offsetting the connecting waveguides so as to reduce the transition loss at the junctions. Such bends were investigated in detail by employing the beam propagation method (BPM) and it was found that they can be optimized with respect to overall loss. In the addition, the S-shaped waveguides and directional couplers with offset junctions were fabricated based on silica-based planar lightwave circuits (PLC) on silicon substrates. The measured insertion losses of these S-shaped waveguides and directional couplers, which are in good agreement with the calculated results, are the lowest thus far reported 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