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Lightwave Technology, Journal of

Issue 2 • Date Feb. 1989

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Displaying Results 1 - 25 of 33
  • Propagation constant of single-mode fibers measured from the mode-field radius and from the bending loss

    Page(s): 225 - 228
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (418 KB)  

    The propagation constant was measured directly using the fiber bending losses (FBI) at different wavelengths, the outcome was compared with the more indirect results of the mode-field radius (MFR) method, and the integration constant determined for the measured wavelengths. This constant was found to be reasonably wavelength-independent. The absolute value rests strongly on the propagation constant model, i.e. on the structure of its empirical formula. As a result it is proposed to use the simple MFR method to determine the relative wavelength dependence of the propagation constant, and to fix its absolute values with only one more complicated FBL measurement at a convenient wavelength.<> View full abstract»

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  • High-voltage sensor employing an integrated optics Mach-Zehnder interferometer in conjunction with a capacitive divider

    Page(s): 229 - 235
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (648 KB)  

    Such devices would be useful for monitoring line voltages in, for example, SF/sub 6/ gas-insulated bus ducts. The theory of the devices is described and the results of tests on a laboratory prototype are presented. Furthermore, the design of a device monolithically integrating a capacitive divider and an integrated-optics Mach-Zehnder interferometer is proposed.<> View full abstract»

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  • Efficient fiber-optic structure with applications to sensor arrays

    Page(s): 236 - 243
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (828 KB)  

    A fiber-optic structure which performs the functions of sensing and telemetry with a minimum of components and with efficient utilization of optical power is described. This structure, referred to as a recursive lattice array, requires N+1 couplers and N fiber sensing loops to realise N sensors. It is shown that for pulsed operation, the duty cycle approaches 100% and the maximum sampling rate is 1/(N+1)T, with T denoting the transit time of a single sensing loop. In the ideal (lossless) case, the power returned to the receiver from any sensor is -10 log 2N referred to the input, compared with previously reported, nonrecursive structures for which this figure-of-merit is -20 log N. Expressions for the optimum coupler tap ratios for two different cases of interest are derived: first, for the case in which all the coupler tap ratios are equal, and second, for the case where they may assume different values. The magnitudes of decaying recirculating terms which add noise to the desired primary returns from each sensor are estimated. Methods for reducing the magnitudes of the undesired terms are outlined.<> View full abstract»

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  • High-efficiency two lens laser diode to single-mode fiber coupler with a silicon plano convex lens

    Page(s): 244 - 249
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (584 KB)  

    A theory for the calculation of the spherical aberration loss of silicon planoconvex lenses is presented. The aberration losses are calculated as a function of the lens parameters. Furthermore, a theory for the coupling efficiency of a laser diode to single-mode fiber for a coupling arrangement consisting of a silicon planoconvex lens and a glass ball lens is given. The theoretical predictions are in good agreement with measurements. Experimentally, a coupling efficiency of 72% (1.4-dB coupling loss) was achieved for a laser diode with farfield angles of 20 degrees *33 degrees FWHM and a not yet fully optimized silicon planoconvex lens.<> View full abstract»

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  • High-accuracy characterization of titanium films for LiNbO/sub 3/ guided wave devices by optical densitometry

    Page(s): 250 - 254
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (440 KB)  

    An experimental study of optical densitometry as a technique for accurate determination of Ti film thickness for integrated optical devices on LiNbO/sub 3/ is discussed. Densitometric data, obtained with a simple instrument for photographic applications, are compared to conventional stylus profilometric measurements and to microgravimetric and Rutherford backscatter measurements; excellent linearity and a sensitivity of about 3 AA are evidenced, as well as capability of absolute calibration in terms of metal atoms per unit surface area, over the entire range of Ti thickness commonly used in integrated optics. The possibility of using this very simple, rapid, and nondestructive method for systematic sample testing, online deposition monitoring, and utilizing optimum coating area is also presented.<> View full abstract»

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  • An on-line fiber drawing tension and diameter measurement device

    Page(s): 255 - 261
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (779 KB)  

    A noncontact online drawing tension meter is described. This meter measures both the drawing tension and fiber diameter during the fiber drawing process. Experimental results show that this meter functions satisfactorily in all aspects of testing. The knowledge of online drawing tension not only helps in the manufacture of fibers with low surface tensile stress, but it also gives information about furnace temperature change and the viscosity of the glass at the neck-down region.<> View full abstract»

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  • Open-loop output and scale factor stability in a fiber-optic gyroscope

    Page(s): 262 - 269
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (705 KB)  

    An all-fiber open-loop, fiber-optic interferometric gyro with polarization-preserving fiber with 14-dB insertion loss and 20-dB polarization extinction is described. The random drift coefficient is 3.2*10/sup -40// square root h for a 1-km coil length on a 16-cm radius. Bias drift is within 0.03 degrees /h over three days. Source coherence effects and optical feedback are shown to result in additional terms in the demodulated output, which can be corrected for. A procedure for obtaining scale-factor coefficients is described. With modeling for temperature and source drive current, these coefficients are measured to be stable within 32 p.p.m. over 12 days.<> View full abstract»

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  • Integrated-optic interferometer position sensor

    Page(s): 270 - 273
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (521 KB)  

    A fully integrated interferometer position/displacement sensor with direction-discrimination capability is discussed. The device is constructed by integrating three kinds of grating components and a pair of photodiodes in a glass waveguide on a silicon substrate and by butt-coupling a single-mode laser diode. Interference signals corresponding to mirror movement were obtained experimentally over a 15-cm range with a 0.39- mu m modulation period.<> View full abstract»

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  • Scalar modes and coupling characteristics of eight-port waveguide couplers

    Page(s): 293 - 296
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (375 KB)  

    The scalar modes and the coupling characteristics of an eight-port waveguide coupler consisting of four parallel single-mode waveguides are discussed. The analysis is based on a rectangular waveguide model which has been known to give accurate results in the case of two waveguide directional couplers. A classification of its various scalar modes is also given.<> View full abstract»

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  • Solution of the scalar wave equation for arbitrarily shaped dielectric waveguides by two-dimensional Fourier analysis

    Page(s): 308 - 313
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (659 KB)  

    A method for calculating the modes of arbitrarily shaped dielectric waveguides is presented. It consists of expanding the field in a two-dimensional Fourier series. The expansion is used to convert the scalar wave equation into a matrix eigenvalue equation. To facilitate calculation of the matrix elements, the waveguide geometry is approximated by a number of rectangles of constant refractive index. The accuracy of the method is demonstrated by calculating the dominant mode of a circular optical fiber and comparing it with the exact solution. The method well-fitted the experimental data on dielectric film waveguides on silicon, including data on waveguide-to-fiber butt-coupling loss, waveguide far-field angles, and the coupling length of directional couplers.<> View full abstract»

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  • Two-stage Fabry-Perot filters as demultiplexers in optical FDMA LANs

    Page(s): 323 - 330
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1311 KB)  

    A high-finesse optical filter can be constructed by cascading two moderate-finesse Fabry-Perot filters of different free spectral ranges. Methods for controlling the undesirable interactions within the interfilter cavity are studied. In particular, the use of an isolator, an attenuator, or a length of fiber longer than the coherence length of the light sources used is considered. The use of a three-mirror filter, which avoids the offending cavity altogether, is also considered. The implications on the number of potential users of optical frequency-division multiple-access (FDMA), local-area networks (LANs) are also addressed.<> View full abstract»

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  • Integrated optical amplifier for fast phase modulated signals

    Page(s): 331 - 335
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (840 KB)  

    The amplifier is based on the optical Kerr effect in waveguides with large third-order nonlinear susceptibility. The short response time of the Kerr effect gives the device an extremely large bandwidth, exceeding that of any laser amplifier. Also, for binary signals, the amplifier is shown to have a phase regenerative effect. Examples of signal and pump powers are given for polydiacetylene waveguides.<> View full abstract»

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  • Dispersion-adapted monomode fiber for propagation of nonlinear pulses

    Page(s): 353 - 357
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    A method of compensating for attenuation in optical fiber systems which uses nonlinear wave propagation (solitons) to achieve high data capacity is discussed. This method is based on adjusting the dispersion parameter of the fiber as a function of the signal intensity along the fiber. A practical implementation of this method, where the fiber is fabricated with variable diameter, continuously adjusted during the drawing is proposed. The fiber tapering necessary to maintain a perfect balance in the nonlinear wave is sufficiently gradual to prevent additional losses. The shape of a signal in the form of an order-one soliton can then be kept invariant. A possible engineering approach where the continuously varying fiber is approximated by discrete sections is suggested.<> View full abstract»

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  • An optical integrated circuit for time-division 2-D velocity measurement

    Page(s): 364 - 367
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (482 KB)  

    An LiNbO/sub 3/ optical integrated circuit pigtailed with two single-mode fibres, which allows time-division two-dimensional velocity measurement, is discussed. To detect time-division multiplexed beat signals corresponding to velocity components v/sub X/ and v/sub gamma / of a moving object, a waveguide switch is integrated on a Z-propagating LiNbO/sub 3/ substrate of 28*7 mm/sup 2/ in addition to a waveguide interferometer with a frequency shifter. In the optical IC, either v/sub X/ or v/sub gamma / could be measured selectively with signal-to-noise ratio of 20 dB by driving an electronic gate placed after a photodiode in synchronization with the waveguide switch.<> View full abstract»

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  • Performance analysis and experiment of a homodyne receiver insensitive to both polarization and phase fluctuations

    Page(s): 368 - 374
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (576 KB)  

    A detailed bit-error-rate analysis of a differential phase-shift keying (DPSK) homodyne receiver which comprises polarization and phase diversities is presented. It is shown that both the requirement for the laser linewidth and the receiver sensitivity are approximately equal to those of a conventional DPSK heterodyne receiver. The insensitivity of the receiver to the polarization state of the incoming signal is also investigated both theoretically and experimentally.<> View full abstract»

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  • Coherent optical multicarrier systems

    Page(s): 375 - 384
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    Optical coherent multicarrier systems with highly selective tunable optical heterodyne receivers can be used for transmission and switching of broadband signals. Some technical solutions for coherent bidirectional subscriber lines, a ten-channel distribution system, and a switching setup with computer-controlled receiver tuning are presented. The laboratory experiments, including carrier-frequency stabilization, multiplexing, and demultiplexing, as well as the fiber components used, are described. The influence of fiber nonlinearities on multicarrier transmission is considered.<> View full abstract»

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  • Design of semiconductor electrooptic directional coupler with the beam propagation method

    Page(s): 385 - 389
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    The design of a low-loss switching voltage double-heterostructure electrooptic coupler switch in III-V semiconductor materials is discussed. The optical propagation is analyzed by the effective index method combined with the beam propagation method. The electrostatic field and electron and hole distributions are analyzed by a numerical simulation. This model is in good agreement with experimental results obtained at 1.56 mu m on directional couplers made of GaAs-GaAlAs DH waveguides and Schottky barrier electrodes.<> View full abstract»

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  • Enhancement of refractive index in Ti:LiTaO/sub 3/ optical waveguides by Zn vapor diffusion

    Page(s): 390 - 392
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    A double diffusion technique to enhance the effective mode index of optical waveguides in LiTaO/sub 3/ is discussed. It consists of Zn diffusion from the vapor phase at relatively low temperatures (750-800 degrees C), into waveguides initially produced by Ti indiffusion at higher temperature (1150-1200 degrees C). Both X- and Z-cut substrates are investigated. A model combines profiles of both diffusions is formulated to calculate the expected effective index values for planar waveguides. Good agreement is found between experimental results and model predictions which assume that the initial Ti profile is not affected by the lower-temperature Zn diffusion. Effective index enhancements as high as 0.005 and 0.003 are obtained by this method for the fundamental extraordinary and ordinary modes, respectively.<> View full abstract»

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  • Performance analysis of coherent optical phase-diversity receivers with DPSK modulation

    Page(s): 393 - 399
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (713 KB)  

    The transmission performance of two phase-diversity receiver structures using a six-port fiber coupler is investigated for coherent optical communication systems with differential phase-shift-keying (DPSK) modulation. A general method for evaluating the error probability of phase-diversity DPSK receivers using delay-and-multiply demonstrators is derived. The method is used to show that, in the shot-noise limited case, the performance of the phase-diversity DPSK receivers is close to that achievable with a heterodyne receiver, provided the frequency offset between lasers is less that about 1% of the bit rate. The allowable total laser linewidth is in the range of 0.3-0.4% of the bit rate.<> View full abstract»

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  • Multimode coupling of unidentical waveguides

    Page(s): 420 - 425
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (624 KB)  

    A system of two parallel slab unidentical waveguides, one a multimode structure and the second a single-mode one, is analyzed using an improved coupled-mode theory. The theory is compared with exact numerical solutions of the complete structure. The comparison is carried out for both TE and TM modes, by evaluating the propagation constants and the normal mode distributions. The approximate propagation constants and the corresponding normal modes are shown to agree very well with the exact solutions. The interdependence between the system parameters and the normal mode patterns is discussed.<> View full abstract»

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  • Single-layer antireflection coating of semiconductor lasers: polarization properties and the influence of the laser structure

    Page(s): 426 - 430
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    Theoretical calculations of the modal reflectance of semiconductor laser facets, giving conditions for the coating index and thickness for a prescribed modal reflectance for TE and TM polarized light, are presented. A simplified method of calculating the modal reflectance is suggested and compared to a more exact method as well as to two other published methods. The possibilities of simultaneously achieving low reflectance for both polarizations are investigated with reference to the laser structure.<> View full abstract»

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  • Laser-to-fiber coupling via optical fiber up-tapers

    Page(s): 274 - 278
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (384 KB)  

    A method for coupling single-mode fiber to laser diodes with high efficiency and greatly reduced alignment sensitivities is discussed. It consists of a spherical ruby lens and a single-mode optical fiber up-taper. Using a double-channel planar buried heterostructure (DCPBH) laser, more than 60% of the light from the lens is coupled into a single-mode fiber via the taper. The lateral and axial tolerances of the lens-taper arrangement are reduced by factors of 20 and 1000 times, respectively, compared with laser coupling to a lensed single-mode fiber. These relaxed alignment tolerances have the potential to allow the taper to interface with a hermetically-sealed laser-lens package via a window and a connector on the package exterior View full abstract»

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  • Short-pulse and high-frequency signal generation in semiconductor lasers

    Page(s): 400 - 419
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    The application of high-speed semiconductors lasers in short-pulse generation by mode locking, gain/Q-switching, and microwave signal generation is reviewed. The underlying basic principles, current state of the art, and areas for further developments are discussed View full abstract»

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  • Phase- and polarization-diversity coherent optical techniques

    Page(s): 279 - 292
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1296 KB)  

    Progress in phase- and polarization-diversity coherent optical techniques has led to impressive receivers able to tolerate wide laser linewidth and large polarization fluctuations. The advantages and the drawbacks of diversity receivers, and recent experimental and theoretical research results are discussed View full abstract»

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  • Statistical approach to the optimization of optical fiber fusion splicing in the field

    Page(s): 431 - 435
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    The optimization of fusion splicing in the field is analyzed and a method for interpretation laboratory splicing data is presented. Two main parameters have been recognized to guide field splicing in long-haul applications: (a) maximum permissible splice loss and (b) maximum number of trials. The influence of these parameters on the average splice loss and on the total number of splices of a well-defined splicing system is illustrated. Computer simulations, based on laboratory test, have been performed to choose the optimum values for the two above-mentioned parameters to minimize the achievable mean splice loss and the number of splices to be made in actual installations 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