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Lightwave Technology, Journal of

Issue 7 • Date Jul 1990

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Displaying Results 1 - 19 of 19
  • Constraints on the bit rates in direct detection optical communication systems using linear or soliton pulses

    Page(s): 1097 - 1106
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    The effects of stimulated Raman scattering (SRS) and the self-frequency shift on soliton communication systems are analyzed. These effects impose stringent limitations on the maximum data rates that can be carried in such systems. The limitations arise as soliton amplitude or frequency fluctuations are translated into pulse position jitter after propagation along a fiber. Estimates of the maximum data rates in single-channel and multichannel soliton systems are obtained and are compared with data rates in linear direct detection systems. A single-channel soliton system can, in principle, carry data at a rate of between two and ten times faster than a simple, direct-detection, linear system. In a multichannel system, using data channels at different wavelengths, the advantages of using solitons are reduced View full abstract»

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  • The radiation response of a Selfoc microlens

    Page(s): 1107 - 1109
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    The radiation-induced darkening of SLW Selfoc microlenses at 810 nm is measured using 100-ns pulses from the Hermes II X-ray simulation machine. Their transmission loss versus total dose is displayed immediately after exposure and 45 μs later, up to a dose of about 32 krds View full abstract»

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  • Effect of phase shift position on spectral linewidth of the π/2 distributed feedback laser diode

    Page(s): 1033 - 1038
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    The dependence of the spectral linewidth on the phase shift position (PSP) of a phase-shifted distributed-feedback (DFB) laser diode is investigated theoretically, using the coupled wave model. In particular, the analysis is performed to find an optimum PSP so as to minimize the spectral linewidth of the laser diode. This optimum PSP is compared to that obtained by maximizing the stability of the laser oscillation. Since both narrow spectral linewidth and good stability are essential for the light source in coherent optical communications, the analysis revealed the suitability of using phase-shifted DFB laser diodes in coherent transmissions View full abstract»

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  • Computer simulation of FSK laser spectra and of FSK-to-ASK conversion

    Page(s): 1110 - 1122
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    The performance of binary frequency shift keyed (FSK) modulated two-segment semiconductor injection lasers is simulated by generating a 64-b pseudorandom step-function bit pattern. This signal, superimposed on a DC bias, is used to drive a two-segment distributed feedback (DFB) laser. To obtain the optical laser spectrum, the input signal is passed through the laser's small-signal transfer function. The resulting spectrum is passed through a Fabry-Perot filter that rejects one of the two principal peaks of the wide-deviation optical spectrum and converts the FSK modulation to amplitude shift keying (ASK) modulation. This simulation determines how different system parameters influence the performance of a laser system used for signal transmission by means of FSK-to-ASK conversion View full abstract»

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  • A statistical design approach for gigabit-rate fiber-optic transmission systems

    Page(s): 1064 - 1072
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    A statistical design approach is proposed for the design of fiber-optic transmission systems (FOTSs). It yields increased regenerator spacings up to about 50% over those provided by the traditional worst-case design. The method involves assuming most of the system parameters to be random variables with known probability distributions. The probability distribution of the regenerator spacing is then numerically found by a Monte Carlo simulation from which the regenerator spacing with a given success probability can be determined. A thorough statistical treatment of attenuation, dispersion, and chirp limits is presented, and the effects of varying the probability density functions of underlying optical system parameters are examined. The numerical results shown demonstrate the repeatability of the proposed statistical design approach View full abstract»

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  • Automation of an optical time domain reflectometer to measure loss and return loss

    Page(s): 1078 - 1083
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    An optical time domain reflectometer (OTDR) is automated to measure transmission loss and return loss of individual faults as well as the entire fiber span. Experimental and field trail results confirm that this technique enables fiber testing and fault locating to be carried out at one location with little or no human intervention View full abstract»

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  • Holographic matched filter for full-field in-line signal processing of optical-fiber sensor outputs

    Page(s): 1039 - 1045
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    A holographic matched filter is used to measure the changes in the output of a dual-mode fiber undergoing axial strain. The hologram is formed by interfering collimated light from a single-mode reference fiber and an unstrained dual-mode sensor fiber on a small piece of holographic material. When the hologram is illuminated by the strained sensor fiber, the cross-correlation field comparing the dual-mode output and its previous state, as recorded in the hologram, is collected, focused into a pick-up fiber, and sent to a photodiode. This arrangement allows for a compact, in-line method for full-field processing of the strain-induced changes in phase and amplitude in the sensor fiber. Other uses of such fiber-based correlators are suggested View full abstract»

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  • Theoretical performance of multigigabit-per-second lightwave systems using injection-locked semiconductor lasers

    Page(s): 1017 - 1022
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    The locking conditions for multigigabit-per-second modulation are examined, and the dependence of the receiver sensitivity on the fiber dispersion coefficient-length product is investigated. With a 4.8-Gb/s NRZ (nonreturn-to-zero) modulation, a 1-dB penalty in receiver sensitivity occurs for a transmission distance of 68 km. The injected power is 0.4 mW and the frequency detuning is -35 GHz. With 10-Gb/s NRZ modulation, the allowable transmission distance is 12.5 km for an injected power of 1.0 mW and a frequency detuning of -35 GHz. These results represent increases in the transmission distances obtained with a solitary laser by factors of 3.7 at 4.8 Gb/s and 2.7 at 10 Gb/s View full abstract»

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  • Correlation-based fiber sensor using a holographic matched filter

    Page(s): 1123 - 1126
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    The principle of a fiber sensor based on an optical correlation technique is described and assessed for its feasibility. The device measures the correlation between the far-field radiation pattern of a multimode sensing fiber and a reference pattern stored in a holographic matched filter. The output is a monotonically decreasing function of the changes in the patterns caused by the perturbance applied to the fiber. The results of some preliminary experiments are discussed and some drawbacks of the technique are pointed out View full abstract»

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  • Silicon MOS amplifier operation in the integrate and dump mode for gigahertz band lightwave communication systems

    Page(s): 1023 - 1026
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    The operation of a MOS amplifier in the integrate and dump mode is discussed. This mode of operation results in the suppression of the input load resistor noise while retaining the advantages of a large dynamic range and no equalization requirement. The technique is useful in improving the receiver sensitivity in circuit topologies such as the nonintegrating front. Several aspects of its MOS implementation are presented, along with test results View full abstract»

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  • Prediction of the gain versus injection-current characteristic of individual semiconductor laser amplifiers

    Page(s): 1055 - 1063
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    A method of calculating the gain versus current characteristic of an individual laser amplifier is presented. The method applies to traveling-wave amplifiers that are derived from semiconductor lasers by antireflectively coating both facets. It relies on a knowledge of certain general parameters, the power versus current characteristics of the laser before and after the first coating has been applied, and a measurement of the residual reflectivity of the first coating. These measurements are normally done during the coating process and therefore require no additional experimental effort. It is found that four parameters, along with a set of fixed general parameters, are sufficient to provide good agreement between calculated and measured results for different lasers View full abstract»

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  • Multipoint operation of two-mode FMWC distributed fiber-optic sensor

    Page(s): 1073 - 1077
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (420 KB)  

    The transmission readout of a dual-mode single-fiber frequency-modulated continuous-wave (FMCW) distributed sensor presents parasitic beat signals when more than one transducer is activated at a time. Experimental evidence of this effect is shown, and a solution for multipoint operation is proposed. This solution is based on the nature of the two types of interference occurring at the fiber end View full abstract»

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  • Bending effects in biconically tapered single-mode fibers

    Page(s): 1084 - 1090
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    Biconically tapered single-mode fibers were fabricated, and their characteristics were studied experimentally. The optical throughput was measured as the fiber was being pulled to produce the required radial profile. The tapered single-mode fiber was bent in a simple fixture, and the optical throughput was measured as a function of the bending angle. It is seen that the bending resulted in very strong oscillations of the optical power as the bend angle was varied. At the point when the light in the core was minimal, the cladding region was bright, indicating that the light has moved to the cladding. The propagation characteristics of the tapered single-mode fiber subjected to bending are analyzed using a stepwise approximation. A simple sensor based on this principle is discussed View full abstract»

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  • Wavelength-division multi/demultiplexer utilizing optically active crystals

    Page(s): 1051 - 1054
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    A wavelength-division multi/demultiplexer (W-MUX/DEMUX) utilizing optically active crystals is proposed and studied. It is shown that using two or more optically active crystals having different rotary powers and dispersions is effective for providing design freedom and for easy assembly of the W-MUX/DEMUX. A design for a two-wavelength W-MUX/DEMUX is also discussed. Based on this design, a W-MUX/DEMUX that multiplexes or demultiplexes light with wavelengths of 0.8 and 1.1 μm was fabricated. The insertion losses are 1.6 and 3.1 dB at wavelengths of 0.8 and 1.1 μm, respectively. Crosstalk attenuation of 13 dB or more is obtained at these wavelengths View full abstract»

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  • High-speed InGaAlAs/InAlAs multiple quantum well optical modulators

    Page(s): 1027 - 1032
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    High-speed modulation over 22 GHz for waveguided InGaAlAs/InAlAs multiple quantum well (MQW) optical modulators is described. A large on/off ratio of over 25 dB is demonstrated with a low-drive voltage (6 V) operating in the 1.55-μm wavelength region. The design and characteristics of MQW p-i-n modulators are discussed. The causes of large-insertion loss and the required drive voltage bandwidth figure of merit for the MQW modulator are discussed. The frequency response measurements show that the response speed is limited by the RC time constant of the device. This suggests that the speed can be further enhanced by decreasing the size and capacitance of the device View full abstract»

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  • Optimum design of δ-doped InGaAs avalanche photodiode by using quasi-ionization rates

    Page(s): 1046 - 1050
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    An avalanche photodiode (APD) designed by using quasi-ionization rates in InP and InGaAs is described. The structure has a δ-doped layer in an InP window layer. The heterointerface electric field is investigated and determined to prevent the tunneling current and carrier multiplication in InGaAs. The gain bandwidth (GB) product of the δ-doped APD is analyzed by R.B. Emmons's (1967) p-i-n electric field method. The highest GB product is 160 GHz View full abstract»

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  • On the shape of bent fiber

    Page(s): 1091 - 1096
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    The general theory for planar bends in a thin fiber with no torsion is derived from a variational principle. The theory is applied to 90° symmetric bends with fixed endpoints and end slopes. Discrete families of bend shapes are discovered, and four are described with the aid of numerically generated examples View full abstract»

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  • Self-phase modulation and dispersion in high data rate fiber-optic transmission systems

    Page(s): 1009 - 1016
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    The theoretical transmission limits imposed by the interaction of first- and second-order group velocity dispersion and intensity-dependent self-phase modulation (SPM) effects for a range of wavelengths around the zero dispersion wavelength (λ0) for fibers in which polarization dispersion is negligible are investigated. It is found that increasing the peak input power to 30 mW reduces the transmission distance for data rates greater than 50 Gb/s, if operating at wavelengths shorter than λ0. Operating at wavelengths longer than λ0 improves the performance due to the cancellation of first-order dispersion by self-phase modulation. For example, at 50 Gb/s and 30 mW peak input power, the maximum transmission distance is 255 and 162 km, if operating at wavelengths 1 nm longer or shorter than λ0, respectively. Above 100 Gb/s, higher-order dispersion limits the transmission distance even at wavelengths equal to, or longer than, λ0. Linear dispersion compensation using a grating-telescope combination can significantly improve system performance for wavelengths where first-order dispersion dominates View full abstract»

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  • Multilevel coherent optical system based on Stokes parameters modulation

    Page(s): 1127 - 1136
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    A multilevel transmission system that allows efficient exploitation of a single-channel bandwidth in coherent optical communication systems is proposed. It is based on Stokes parameter modulation and a decision on the Poincare sphere. The block scheme of the transmitter, which is able to provide a generic output state of polarization (SOP) starting from a linearly polarized optical field, is shown and described. The propagation along the fiber is described in order to derive the expression of the optical field at the receiver input. The spectral characteristics of the transmitted and the received optical signals are analyzed 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