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Lightwave Technology, Journal of

Issue 3 • Date Mar 1995

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Displaying Results 1 - 25 of 26
  • Analysis of dielectric guides by transverse magnetic field finite element penalty method

    Page(s): 442 - 446
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (344 KB)  

    The main purpose of this paper is to use the finite element method using a penalty function formulation to solve the vector wave equation with transverse H-field formulation together with the boundary operator. We impose continuity conditions on the boundary interfaces for both E z and Hz components. We apply this technique to obtain the propagation constant for a three-layer ridge structure and a multiple quantum well ridge guide as examples, and a comparison with previously published results shows excellent agreement View full abstract»

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  • Characteristics of linewidth-narrowed distributed Bragg reflector lasers with a fiber external cavity formed with the vertical grating emission

    Page(s): 356 - 363
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    Linewidth reduction has been observed in a distributed Bragg reflector (DBR) laser with a second-order grating when an external cavity is formed with the vertical emission. The external cavity consists of a length of optical fiber which is brought close to the top of the laser. Displayed linewidths as low as 26 kHz have been measured. To the authors' knowledge, this is the first report of linewidth reduction via vertical emission from a laser diode View full abstract»

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  • A new general approach to optical waveguide path design

    Page(s): 481 - 492
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    This paper introduces a new general approach to waveguide path design. We propose an alternative approach to the usual concatenation of offset line segments and arc of circles that is geometrically less constrictive and more versatile. We also propose an adapted pure bend loss reduction mechanism that relies on a continuous widening of the waveguide together with the reduction of transition loss through curvature adaptation. The numerical results presented here show that this method can improve the loss figures and ease the burden of waveguide path design. Moreover, because of its continuous nature, the proposed approach is intrinsically less dependent on wavelength than the usual concatenation technique View full abstract»

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  • An improved optical heterodyne DPSK receiver to combat laser phase noise

    Page(s): 525 - 533
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (776 KB)  

    Presents a method to improve the performance of a standard delay-and-multiply type optical heterodyne binary-DPSK receiver. This is achieved by using separate “weighting” bandpass filters to shape the phase noise corrupted direct and delayed signals before combining and decoding as for the standard receiver. The optimization of a filter parameter allows this “weighted” receiver to exhibit a lower phase noise sensitivity than the standard receiver. The most significant achievement of the weighted receiver is the ability to tradeoff excess signal power to obtain low bit error rates when large amounts of phase noise are present View full abstract»

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  • Fourier decomposition method applied to mapped infinite domains: scalar analysis of dielectric waveguides down to modal cutoff

    Page(s): 375 - 383
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (860 KB)  

    By transforming the infinite x-y plane onto a unit square and using two-dimensional Fourier series expansions, the modal fields and propagation constants of dielectric waveguides are accurately determined within the scalar (weak-guidance) regime. The new method is reliable down to modal cutoff and gives cutoff V-values directly. Numerical cutoff values for the LP11 modes of square- and rectangular-core waveguides are determined as a function of core aspect ratio, and are found to agree with those obtained by the finite element method to within 0.1% View full abstract»

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  • A scalar variational analysis of rectangular dielectric waveguides using Hermite-Gaussian modal approximations

    Page(s): 493 - 506
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    A scalar variational analysis of rectangular dielectric waveguides using Hermite-Gaussian modal approximations is presented. The technique analyzes waveguides by finding a closed-form, approximate solution to the given problem. We begin with an assumed, closed-form field solution, with unknown parameters which can be chosen to best match the assumed field to the actual field solution using variational principles. The values of the unknown parameters of the assumed field are determined by solving a set of simultaneous equations, not by a search method. As a result, this analysis method is computationally fast. Another benefit is that this method gives best-fit, closed-form modal approximations View full abstract»

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  • Design and evaluation of an optically triggered monolithic sample and hold circuit using GaAs MESFET technology

    Page(s): 422 - 429
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    The design and evaluation of an optically triggered, fully integrated sample and hold circuit (OS/H) is described. Measured results are presented that demonstrate operation of this circuit at 250 Ms/s and with effective resolution approaching 8 bits. The integrated circuit, which measures 2.1 mm×1.4 mm, is realized in -1.0-V threshold, 20-GHz ft GaAs MESFET technology, consumes approximately 200 mW of power, and requires one optical address. The OS/H will find applications in high precision, hybrid, and integrated signal processing systems where high speed, high levels of parallelism, and low timing jitter are important. Measured results of a series photoconducting (Auston switch) OS/H realized in the same technology are presented for comparison purposes View full abstract»

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  • TM modes guided by nonlinear dielectric slabs

    Page(s): 391 - 395
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    Propagation of a TM0 mode in a Kerr-type nonlinear dielectric slab is investigated. The exact analytical expression of E 2(x), E2=Ex2+EZ 2, the decoupled linear differential equation and its equivalent Volterra integral equation of Ex, and the eigenvalue equation of propagation constant β are presented. Finally, an example of approximate analytical solutions obtained by the method of successive approximation is given View full abstract»

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  • Optimal design for broadband quasi-phase-matched second-harmonic generation using simulated annealing

    Page(s): 456 - 460
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    We propose a modulation-optimization method for achieving broadband quasi-phase matching in second-harmonic generation devices with domain-inverted structures. Using simulated annealing, we optimize phase-matching curves tailored to practical purposes by appropriately choosing a cost function in the annealing process. Both the acceptance bandwidth and the conversion efficiency are significantly improved in comparison with conventional periodically domain-inverted devices View full abstract»

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  • Tapered acoustical directional couplers for integrated acousto-optical mode converters with weighted coupling

    Page(s): 364 - 374
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    Weighted coupling for strong sidelobe suppression of integrated acoustooptical mode converters in LiNbO3 using acoustical directional couplers has been studied theoretically and experimentally. A parameter free model for the propagation of surface acoustic waves in guiding structures has been developed based on a step-like variation of the acoustic velocity. Comparisons of theoretical results with experimental ones for acoustic waveguides and directional coupler structures confirm the applicability of the model. A coupled mode description of the acousto-optical polarization conversion in converters with acoustical directional couplers has been developed and applied to several tapered acoustical directional couplers. The model reveals that the conversion characteristics are usually strongly asymmetric. If the directional coupler is appropriately designed, a sidelobe suppression of about 30 db can be achieved. First experimental results with tapered directional couplers confirm within some limits the theoretical predictions View full abstract»

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  • Analysis on state of polarization of stimulated Brillouin scattering in an optical fiber ring-resonator

    Page(s): 384 - 390
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (504 KB)  

    As a basic study of a Brillouin fiber-optic gyro, the state of polarization of stimulated Brillouin scattering in an optical fiber ring-resonator is analyzed. A high-birefringent fiber ring-resonator with 90° polarization axis rotation at the splice is considered as a candidate to have a stable lasing. It has two special states of polarization as the lasing modes, namely the polarization lateral modes. The lasing frequencies, namely the longitudinal modes for one state are fixed just in the middle point between the two neighboring lasing frequencies for the other in this resonator. This means that the stable single mode lasing may be obtained. The lasing threshold, the alternation of the lasing modes are discussed both by the simplified theory and the strict theory View full abstract»

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  • Optical code-division-multiplexed systems based on spectral encoding of noncoherent sources

    Page(s): 534 - 545
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (912 KB)  

    Presents a new category of optical CDMA systems which work based on spectral encoding. In such systems, that the authors refer to as frequency-encoded CDMA (FE-CDMA) systems, the coding is done in the frequency domain while in the usual CDMA systems the code multiplies the modulation signal in the time domain. They present a new type of FE-CDMA system, based on encoding noncoherent broadband sources. They discuss the advantages of the system compared to other optical CDMA systems and present its performance. They show that very efficient, low-cost, CDMA systems can be obtained with an aggregate throughput of many gigabits per second. Also, for this system, the spreading gain of CDMA is independent of the modulation bandwidth. Hence, the system can accommodate variable bit rates, naturally View full abstract»

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  • Full-vector waveguide modeling using an iterative finite-difference method with transparent boundary conditions

    Page(s): 465 - 469
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (408 KB)  

    We describe a finite difference solution technique for the full-vector waveguide equation based upon the alternating-direction-implicit (ADI) iterative method. Our technique accurately treats dielectric boundaries (including corners), requires minimal computer resources, and executes faster (by factors of 3-10) than other iterative approaches. In addition, we employ a transparent boundary condition that effectively removes the sensitivity of the calculated results to the size of the computational domain. This feature greatly facilitates the examination of modes near cutoff View full abstract»

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  • Transient simulation of heterojunction photodiodes-part I: computational methods

    Page(s): 396 - 405
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    A novel approach is presented for incorporating the transient solution of one-dimensional semiconductor drift-diffusion equations within a general circuit simulation tool. This approach allows simple representation of localized carrier transport models of simulated devices through equivalent circuit elements such as voltage controlled current sources and capacitors. It also lends itself to mixed-mode transient simulation of devices and circuits. The utility of the new simulation approach in state-of-the-art device design is demonstrated by the transient response analysis of a GaAs heterojunction p-i-n photodiode, and by the time-domain analysis of an integrated photoreceiver circuit View full abstract»

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  • Single-polarization fiber lasers using Bragg gratings in Hi-Bi fibers

    Page(s): 350 - 355
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    Cavities of high birefringence (Hi-Bi) Nd3+ doped fiber lasers have been closed by an intracore Bragg grating reflector and a dichroic mirror. The spectral characteristics of the laser emissions have been investigated using a measurement accuracy of 100 MHz. Two oscillating frequencies corresponding to two orthogonal linear polarization states of the laser emissions have been observed. The orientations of the two linearly polarized emissions were found parallel to the Hi-Bi fiber axes, respectively. Laser thresholds, slope efficiencies and differences between these frequencies were found to depend on the conditions of the Bragg grating inscription. Multimode single polarization Hi-Bi fiber lasers using two Bragg gratings were fabricated and characterized for the first time to our best knowledge. Wavelength tuning of this single polarization fiber laser has been demonstrated under temperature rise of the two gratings. Polarization and frequency stabilities of the emissions from these Hi-Bi fiber lasers were studied and compared to those from lasers built in a conventional fiber (fiber with no polarization holding property) View full abstract»

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  • High-performance compact optical WDM transceiver module for passive double star subscriber systems

    Page(s): 517 - 524
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    High-performance transceiver-type optical WDM interface modules with a volume of only 36 cc have been developed for PDS subscriber systems. The new module comprises an optical WDM sub-module, hybrid-integrated transmitter and receiver circuits. In the WDM sub-module, a planar lightwave circuit chip was hermetically sealed together with laser and photodiode chips in order to minimize the size of the transceiver module. The lightwave circuit was formed on an optical-waveguide chip by adopting a high-silica based optical-waveguide technology. The circuit has a 3-dB directional coupler for bi-directional transmission with a 1.3-μm wavelength through a single fiber and a wavelength division multiplexer between both 1.3-μm and 1.55-μm wavelengths. The overall characteristics of the fabricated WDM sub-module achieved were a responsitivity of 0.25±0.05 A/W, an insertion loss approximately 3 dB at 1.55 μm and an isolation of 35 dB between both wavelengths. Optical output power of the fabricated transceiver module was -3.8 dBm. Also, receiver sensitivity of less than -35 dBm with an overload of over -14 dBm were obtained by introducing high-speed automatic gain and threshold control techniques. Thus, an allowable span loss of over 30 dB and an optical dynamic range of over 20 dB were attained. The preamble bit length required to reach stable receiver operation was confirmed to be within three bits View full abstract»

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  • Guided-wave characteristics of optical graded-index planar waveguides with metal cladding: a simple analysis method

    Page(s): 416 - 421
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    The guided mode characteristics of metal-clad graded-index waveguides are generally determined by complex eigenvalue equations or perturbative methods. However, these methods either require several iterations in the complex plane or are only suited to the class of waveguides whose guided field can be described analytically. We describe a method of calculating complex propagation constants for metal-clad graded-index waveguides under very general but weakly guiding conditions. The method, based on Galerkin's formalism using trigonometric basis functions, allows arbitrary inhomogeneous and complex refractive index profiles. Applications to three generally used waveguide models show our approach to be in good agreement with other analytical or numerical methods View full abstract»

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  • Measurement of the facet modal reflectivity spectrum in high quality semiconductor traveling wave amplifiers

    Page(s): 430 - 433
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    We demonstrate that the Hakki-Paoli technique, commonly used for measuring single pass gain in semiconductor lasers, can be modified to measure facet modal reflectivity down to 10-6 in semiconductor laser amplifiers. We also introduce a new technique based on Fourier and Hilbert transformations of the spontaneous emission spectrum (the SET method) which enhances the signal-to-noise ratio and permits modal reflectivity measurements down to 10-1 View full abstract»

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  • Transmission characteristics of arrayed waveguide N×N wavelength multiplexer

    Page(s): 447 - 455
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (708 KB)  

    To realize practical wavelength division multiplexing (WDM) systems, a high-performance N×N wavelength multiplexer is introduced that is based on an arrayed-waveguide grating. Its transmission characteristics are theoretically derived and experimentally confirmed. A prototype is constructed using the previously proposed techniques that attain low insertion loss and polarization independent operation. It has 16 channels (N=16) with a spacing of 0.8 mn, or 100 GHz, in the 1.55-μm band. Frequency relation between input and output ports, free spectral range, and passband width are determined. A demonstration of IM-DD pulse transmission shows that there is no degradation of bit error rate resulting from the finite passband width and crosstalk of the multiplexer. It is confirmed that the multiplexer can realize highly reliable N-channel WDM and WDM-based N×N interconnect optical networks View full abstract»

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  • Transient simulation of heterojunction photodiodes-part II: analysis of resonant cavity enhanced photodetectors

    Page(s): 406 - 415
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (872 KB)  

    The high-speed response properties of resonant cavity enhanced (RCE) photodetectors have been investigated. The limitations on the high-speed performance of photodiodes and the advantages of RCE-detection are discussed. Transient response of heterojunction photodiodes under pulsed optical illumination has been simulated using the method described in Part I. Results on conventional AlGaAs/GaAs and RCE GaAs/InGaAs heterojunction p-i-n photodiodes are presented. For small area detectors, almost 50% bandwidth improvement along with a two-fold increase in efficiency is predicted for RCE devices over optimized conventional photodiodes. A nearly three-fold enhancement in the bandwidth-efficiency product was shown View full abstract»

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  • Optical bandwidth considerations in p-i-n multiple quantum-well modulators

    Page(s): 461 - 464
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    We investigate the optical bandwidth of p-i(multiple quantum well [MQW])-n modulators employing various MQW designs. The optical bandwidth translates directly into an operating temperature range due to the shift of the band gap with temperature. We find that although greater maximum modulation may be obtained with narrow (~90 Å) quantum wells operating below the band edge (absorption increases with field), uniform large performance may be obtained over a larger bandwidth using wider (~110 Å) quantum wells operating at the exciton (absorption decreases with field). We obtain a usable bandwidth of 7.7 nm, which translates into a operating temperature range of 27°C View full abstract»

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  • Improved spectral characteristics of MQW-DFB lasers by incorporation of multiple phase-shifts

    Page(s): 434 - 441
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    The single-mode stability of strained-layer MQW-DFB lasers with electron-beam written gratings containing zero, one and three phase-shifts, and with a relatively large coupling strength, has been investigated theoretically and experimentally. The fabricated lasers with the multiple phase-shifted (MPS) structure exhibited a higher degree of stability than the λ/4-shifted lasers, and a considerably improved stability for both categories with phase-shifts compared to the nonshifted lasers was obtained. These results were in good agreement with our simulations. An investigation of the linewidths of the phase-shifted lasers is also presented. The MPS lasers had a significantly lower linewidth floor (down to 600 kHz) than those with one phase-shift. There was no degradation of the side-mode suppression-ratio correlated to the linewidth floor or rebroadening. A possible explanation for the lower linewidth floors obtained for the MPS lasers is that this structure is less sensitive to inhomogeneous carrier fluctuations. Longitudinal fluctuations in the shape of the photon density distribution will thereby be suppressed View full abstract»

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  • Capacity of broadcast channels in the near-future CATV architecture

    Page(s): 507 - 516
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    Reports fundamental information theoretic results for near-future CATV downstream digital distribution networks. The CATV industry is evolving to this network architecture to quickly replace plant that would otherwise be left with serious reliability problems owing to deployment of cascades of electronic amplifiers. This new architecture is composed of a passive fiber trunk feeding COAX branches altogether serving about 200 homes. Frequency-division-multiplexed digital signals subcarrier intensity modulate a laser illuminating a single-mode fiber. Only one (electronic) amplifier is used and it is located at the COAX feed. Aside from additive white Gaussian noise (AWGN) from shot noise exacerbated by the amplifier, a significant impairment is the clipping stemming from the intensity modulation. A dimensionless parameter identified as key to describing channel capacity is I0/(qFB) where I0 (0.01 to 1 mA) is the photocurrent delivered, q is electron charge, F (10 log F=2 to 10 dB) is the electronic amplifier effective noise figure and B (200 MHz to 1 GHz) is the overall system bandwidth. The following are reported: the optimal design of the head end where signals are launched, availability of extraordinarily high capacities, and how a hefty fraction of capacity might be achieved View full abstract»

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  • Evaluation of parasitic upconversion mechanisms in Er3+-doped silica-glass fibers by analysis of fluorescence at 980 nm

    Page(s): 341 - 349
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    The behavior of modulated and unmodulated upconversion fluorescence in Er3+-doped silica-glass optical fibers pumped at 1480 nm has been experimentally and theoretically investigated. It is found to be consistent with a model where the upconversion fluorescence is generated by homogeneous and inhomogeneous energy-transfer upconversion. Model calculations indicate an upper limit of a homogeneous upconversion coefficient of 10-23 m3/s in fiber, and a negligible cross-section for excited-state absorption at 1480 mn View full abstract»

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  • A simplified dispersion limit formula for IM/DD systems and its comparison with experimental results

    Page(s): 546 - 550
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (328 KB)  

    A simplified formula for the dispersion limit of single-mode-fiber intensity modulation/direct detection (IM/DD) systems is derived for arbitrary given normalized pulse width U, eye opening penalty X and source linewidth enhancement factor α. From the comparison with published theoretical analyses, computer simulation and experimental data, its validity and the limits of existing formulae are shown. Using this simple and general formula, one can easily obtain the dispersion limit of various fiber types under different working conditions in IM/DD systems 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