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Lightwave Technology, Journal of

Issue 7 • Date Jul 1991

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Displaying Results 1 - 18 of 18
  • A broad-band single polarization optical fiber

    Page(s): 817 - 820
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    The authors report on a single-mode optical fiber that transmits one and only one polarization state of the fundamental mode over a broad wavelength band (13%). The good broadband performance is attributed to the fiber's refractive-index profile, which mathematically allows only one polarization state to cutoff. The authors discuss general design principles and show that the mode field diameter is a qualitative indicator of the fiber's performance. The fiber's guided polarization state is similar to the fundamental mode of a step-index fiber in its low attenuation, 5.5 dB/km, and small mode diameter, 5.8 μm (both measurements at 840 nm). Most important, the fiber shows a broad single polarization band, 13%, a feature well described by the change in mode field diameter with wavelength of an ideal, circularly symmetry, W -profile fiber View full abstract»

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  • Polarization mode dispersion of short and long single-mode fibers

    Page(s): 821 - 827
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    Polarization mode dispersion (PMD) in short and long single-mode fibers was measured by a polarization-maintaining Michelson interferometer. A nonnegligible PMD was found in some standard fibers. The sensitivity enables PMD to measure the bend-induced PMD of a fiber rolled on a 28-cm diameter drum. A theoretical model for PMD with random mode coupling is developed, and an explicit equation for the time-of-flight distribution is presented. Comparison between measurements on short and long fibers with residual birefringence leads to an estimation of the coupling length on the order of 20-30 m View full abstract»

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  • Integrable semiconductor optical correlator, parametric spectrometer for communication systems

    Page(s): 906 - 917
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (932 KB)  

    A broadband integrable waveguide correlator and parametric spectrometer is analyzed both theoretically and experimentally. The correlator can measure pulsewidths from subpicosecond to tens of picoseconds centered at wavelengths of 1.06 to 1.7 μm without any mechanical alignment. The parametric waveguide spectrometer is shown to resolve not only the mode of a 1.3-μm Fabry-Perot laser diode but also the shift of the modes as a function of bias current. The improvement of these integrable waveguide structures and their possible use in laser stabilization, the defining of fixed frequency channels, and other applications for coherent communication systems are also discussed View full abstract»

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  • Single-mode fused biconical coupler optimized for polarization beamsplitting

    Page(s): 853 - 858
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (452 KB)  

    A single-mode fused biconical coupler for polarization beamsplitting is described. In the coupling region, standard communication fibers are used. The output fibers are polarization-maintaining. To stop the coupler drawing process accurately, the degree of polarization is measured during the drawing and is used as a criterion. Losses of 0.2 dB are typical, and a minimum extinction ratio of -27 dB is achieved. A usable spectral window as broad as 17 nm with an extinction ratio smaller than -15 dB for both output fibers is obtained. Any specified wavelength for the minimum of the extinction ratio is reached within ±3 nm View full abstract»

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  • Reduction of spectral noise density in p-i-n-HEMT lightwave receivers

    Page(s): 887 - 892
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (392 KB)  

    The spectral noise density of a lightwave receiver is computed from known physical parameters of the photodiode and the high-electron-mobility transistor (HEMT). Low noise is achieved for an appropriate choice of device parameters. The results are applied to circuits built with readily available commercial HEMTs and p-i-n photodiodes. They also predict the superior noise performance of cooled receivers which cannot be readily derived from previous work View full abstract»

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  • Matrix algebra for all-fiber optical resonators

    Page(s): 838 - 844
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    A method for calculating the output intensities of passive optical resonators including fiber couplers is presented. The method is based on matrix algebra and is sufficiently general to consider cavities using several couplers. A 4×4 format is used which incorporates matrices for the action on the fields of both the coupler and the geometry developed around the coupler. The validity of this method is first tested on two well-known optical fiber devices. Then a double Fox-Smith resonator is investigated, and the results exhibit both high-frequency selectivity and high finesse. A potential application to single-longitudinal-mode operation of rare-earth-doped fiber lasers is also discussed View full abstract»

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  • Properties of commercial 1.3-μm Fabry-Perot laser modules in a time compression multiplexing system

    Page(s): 918 - 923
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    The practical properties of nine types of 1.3-μm Fabry-Perot laser modules were determined so as to construct a bidirectional transmission system. Time compression multiplexing (TCM) transmission is employed and the modules must act as both transmitter and receiver. Many modules are tested and it is found that the responsivity of a laser module is roughly proportional to the module's output power. The main source of variation in responsivity is determined to be due to coupling effects. Optical characteristics are measured over the range -15 to +65°C. The maximum transmission distance for narrow-band ISDN (integrated services digital network) services over single-mode fibers is determined for a bit rate of 3.5 Mb/s View full abstract»

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  • Design parameters for fluoride multimode fibers

    Page(s): 828 - 831
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (304 KB)  

    Numerical calculations of losses due to polymer coatings and macrobending have been made for step-index multimode fluoride fibers. To minimize such losses, fiber parameters must be chosen to give a large value for V, the normalized frequency. Due to the long propagation wavelength (2.5 μm) for fluoride fiber, the parameters needed are very different from those of silica fiber. Using the criterion that ⩾90% of the modes have losses ⩽0.01 dB/km, it was found that the cladding diameters need to be rather large compared to step-index silica fiber parameters. Although the mode distributions are unknown for fluoride fiber, using a theoretical Gaussian distribution, losses were calculated for the various fiber parameters View full abstract»

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  • Coupling of periodic modes

    Page(s): 859 - 863
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    The author examines the effect of a periodic perturbation on a periodic structure, taking linear twin-core couplers with an axially periodic refractive index as examples. The focus is on the coupling effect of the normal periodic modes of a periodic structure under a sinusoidal perturbation, since any periodic function can be represented by a Fourier series. A perturbation to an ideal waveguide structure, is shown to lead to coupling of the normal modes of the structure. For an ideal periodic structure (such as a twin-core nonlinear coupler at a fixed excitation and power), a periodic perturbation to the structure gives rise to coupling of the normal periodic modes of the structure View full abstract»

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  • WDMA/subcarrier-FDMA lightwave networks: limitations due to optical beat interference

    Page(s): 931 - 943
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    The authors present a general model of optical beat interference, and its contribution of channel outage in a WD-SFDMA (wavelength division-subcarrier frequency division multiple access) network. The probability of channel outage due to optical beat interference is determined from analysis and computer simulation for externally and directly modulated single-mode lasers. These results are used to calculate the ultimate limitation on the throughput and capacity of the network due to beat note interference, for a simple retransmission protocol. It is shown that, as more subcarrier channels are added, network capacity increases sublinearly and eventually saturates View full abstract»

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  • Nonorthogonal coupled-mode theory of grating-assisted codirectional couplers

    Page(s): 845 - 852
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    Grating-assisted codirectional couplers are analyzed by a nonorthogonal coupled-mode theory. The coupled-mode equations are solved exactly, and the effects of all the space harmonics generated by the periodic gratings are included in the analysis. More rigorous relations among the grating period, the grating height, and the coupling length are established. The power exchange between the guides is investigated as a function of the propagation distance and the wavelength. A comparison with previous approximate solutions is made and discussed View full abstract»

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  • Performance of single-electrode 1.5-μm DFB lasers in noncoherent FSK transmission

    Page(s): 924 - 930
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    The author reports the results of an investigation of the performance of single-electrode 1.5-μm DFB (distributed feedback) lasers in 1.7-Gb/s noncoherent frequency-shift-keyed (NC-FSK) transmission. Sixteen commercial laser transmitters were characterized in terms of FSK transmission sensitivity, eye-margin, chromatic dispersion penalty and pattern dependence. Using amplitude-shift-keying (ASK) performance as a baseline, FSK is shown to outperform ASK when dispersion is present, while ASK is slightly better with no dispersion. FSK transmitters with commercial single-electrode DFB lasers are shown to provide an attractive alternative to ASK in dispersion limited systems. The FSK degradations mainly result from an inadequate FM modulation index and a thermal-FM index manifested as a pattern length dependence View full abstract»

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  • A polarization splitter on LiNbO3 using only titanium diffusion

    Page(s): 879 - 886
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    A novel polarization splitter is proposed for use in integrated optical circuits on lithium niobate. In contrast to previously reported devices, its operation is based on the mode sorting effect with no external control, while its fabrication requires only a single technology: the diffusion of titanium. The splitter is formed by a Y junction. The polarization splitting can be achieved by making the output waveguides from two titanium strips with different dimensions. A realistic design of these output guides is presented, and some technological aspects are discussed. The operation of the polarization splitter is investigated with the beam propagation method. The results show that a 15-dB extinction ratio is obtained with branching angles larger than 0.2°. The extinction ratio can be as high as 30 dB with a branching angle of 0.1°. The excess losses are below 0.05 dB View full abstract»

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  • 4×4 GaAs/AlGaAs optical matrix switches with uniform device characteristics using alternating Δβ electrooptic guided-wave directional couplers

    Page(s): 871 - 878
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    Integrated 4×4 GaAs/AlGaAs optical matrix switches constructed from 12 electrooptic directional couplers have been realized. In order to achieve uniform device characteristics, molecular beam epitaxy and reactive ion beam etching were chosen as the crystal growth technique and waveguide fabrication technique, respectively, in addition to the simplified tree structure as a matrix switch architecture. As a result, matrix switches with quite uniform device characteristics, such as small switching voltage deviation and little path dependence in ±0.5-dB propagation loss, have been realized View full abstract»

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  • Coupling of modes in bent biconically tapered single-mode fibers

    Page(s): 832 - 837
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (468 KB)  

    Biconically tapered single-mode fibers are fabricated by heating a single-mode fiber while applying tension. As a result of this tapering, cladding modes are excited in the tapered region of the fiber where the V parameter of the fiber goes down below 1.0. These cladding modes couple to one another, leading to fluctuations of the optical throughput. Since the index difference between the cladding and the external medium is rather high (~0.5), the cladding modes will be of the exact type, namely, TE, TM, HE, and EH modes. The coupling of these modes in the tapered region is analyzed using the exact mode formalism when the tapered region is bent. The theoretical results agree very well with experimental results obtained on bent tapers which show strong fluctuations of the optical power as a function of the bending angle View full abstract»

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  • Delta-doped avalanche photodiodes for high bit-rate lightwave receivers

    Page(s): 900 - 905
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    The authors estimate the GB (grain bandwidth) product limits and the noise performance of a new SAGM-APD (separate avalanche, grating, and multiplication avalanche photodiode) structure: the δ-doped SAGM-APD. It is shown that GB products in excess of 140 GHz for a 0.2-μm-thick multiplication layer and possibly larger GB products for smaller widths can be obtained. While recent calculations have predicted increased GB products for this δ-doped SAGM-APD structure, the authors explicitly prove using conventional theory that this is possible only with a concomitant increase in the multiplication noise. It is further demonstrated that it is essential to optimize the width of the multiplication layer for a given bit-rate to achieve minimum multiplication noise consistent with a GB product high enough to accommodate the requisite frequency response at the optimum gain. It is shown that the δ-doped SAGM-APD structure is a very good candidate for high bit-rate receiver applications View full abstract»

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  • Theoretical modeling and characterization of annealed proton-exchanged planar waveguides in z-cut LiNbO3

    Page(s): 864 - 870
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    Planar optical waveguides in z-cut LiNbO3 fabricated by the annealed proton-exchange technique using pure pyrophosphoric acid as the initial proton source have been investigated. A generalized Gaussian function was used to accurately model the refractive-index profile, resulting in considerable improvements over previous work. The nonlinear dependence of the index on the proton concentration was verified by directly calculating the change in the area under the index versus depth curves. Annealing was found to allow for flexibility in the tailoring of the waveguide parameters. An empirical correlation of the changes in these parameters with the fabrication conditions was achieved through the use of a general power law View full abstract»

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  • A multichannel grating cavity laser for wavelength division multiplexing applications

    Page(s): 893 - 899
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    A novel form of wavelength selectable diode laser source is proposed for wavelength division multiplexing (WDM) applications. The source may be used to operate at specific wavelengths across the complete gain spectrum of the laser diode material, but does not require any moving parts. Theoretical simulations indicate that the device can be expected to operate in a single longitudinal mode for channel separations on the order of 1 nm. The potential of using the device to generate parallel streams of WDM data is considered 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