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Lightwave Technology, Journal of

Issue 4 • Date April 1989

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Displaying Results 1 - 24 of 24
  • BER evaluation for phase and polarization diversity optical homodyne receivers using noncoherent ASK and DPSK demodulation

    Page(s): 584 - 599
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    An analysis of the performance of phase diversity receivers using amplitude-shift keying (ASK) and differential phase-shift keying (DPSK) is presented. Both (2*2) and (3*3) multiport receivers are investigated. Asymptotic methods are used to estimate the bit error rate (BER) and signal-to-noise power ratio (SNR) dependence for each type of the receiver. The analysis favors the squarers as the demodulators for ASK whose performance approaches that of the ideal heterodyne detector in the limit of large SNR. A modification of the ASK ((3*3)) receiver which cancels the local oscillator intensity noise is proposed. Receivers which comprise polarization and phase diversity techniques are also investigated for both ASK and DPSK. Their performance is independent of the polarization state of the received signal, and the value of SNR required to obtain the BER of 10/sup -9/ is only a few tenths of a decibel greater than that needed by the phase diversity receivers.<> View full abstract»

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  • Ti-LiNbO/sub 3/ waveguide serrodyne modulator with ultrahigh sideband suppression for fiber optic gyroscopes

    Page(s): 600 - 606
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    The theoretical and experimental performance of guided-wave serrodyne phase modulators formed through indiffusion of Ti and LiNbO/sub 3/ substrates is discussed. Basic serrodyne theory is reviewed and a modified model of the serrodyne modulator incorporating effects of polarization, light-source coherence, device response time, and device-related intensity modulation is developed. Sources of modulation errors and harmonic suppression limitations imposed by each are identified. Experimental results showing greater than 50-dB suppression to 200-kHz ramp frequency and correspondence to expected limitations are then presented. Good agreement between theory and experiment is found. The results indicate that very high suppression, greater than 60 dB, at frequencies to several hundred kilohertz are possible with Ti-LiNbO/sub 3/ waveguide devices.<> View full abstract»

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  • A simple 8*8 optoelectronic crossbar switch

    Page(s): 607 - 614
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    The authors demonstrate the operation of an 8*8 optoelectronic crossbar switch consisting of integrated arrays of eight 1*8 GaAs metal-semiconductor-metal (MSM photodiodes connected in a current summing network to the input of Si bipolar transimpedance amplifiers. The MSM devices are also connected to TTL transistor-transistor logic) driven CMOS analog multiplexers which, in the 'off' state, switch the detectors into an open-circuit mode. This particular combination of detectors and switching network gives a very high interchannel isolation, reduced circuit complexity, and low input noise. Data rates of 200 Mbit's and switch reconfiguration times of -100 ns are achieved. System noise is calculated and measured, and the advantages of using fully integrated GaAs crossbar switch arrays are quantitatively discussed.<> View full abstract»

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  • Angle-tuned etalon filters for optical channel selection in high density wavelength division multiplexed systems

    Page(s): 615 - 624
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    Applications are discussed for angle-tuned in-line Fabry-Perot etalons for optical channel selection in a high-density wavelength division multiplexed (WDM) direct-detection fiber system. A typical WDM application (LAMBDANET type) was described. Different demultiplexing techniques and their relative advantages were considered. Design guidelines are given for determining the etalon parameters, the minimum channel spacing and the maximum number of channels for a single etalon and multiple etalons, including stacked identical etalons and stacked nonidentical etalons. Experimental results on using these etalons for optical channel tuning in a multiwavelength WDM optical communication system are presented.<> View full abstract»

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  • Power partition fluctuations in two-mode-degenerate distributed-feedback lasers

    Page(s): 632 - 639
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    Measurements are presented along with a theoretical analysis of power partition fluctuations in a distributed feedback (DFB) laser operating in continuous wave with the two DFB degenerate modes as the only significant longitudinal modes. The power ratio of the two modes was varied from 1.1 to 2500:1 by electrical control using a two-electrode DFB laser. The laser was observed to exhibit (1) transient power dropouts and (2) two-mode relaxation oscillation. The dropout depths were less than 30% of the main-mode power in all cases, except when the laser was subjected to external optical feedback. The relaxation oscillations of the two-mode power are anticorrelated, which is different from the relaxation oscillation of the total power due to photon-carrier interaction. The calculated result based on a Fokker-Planck analysis agrees with the experiment, except for the two-mode relaxation oscillation, which was not considered in the theory.<> View full abstract»

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  • 2-Gbit/s signal amplification at lambda =1.53 mu m in an erbium-doped single-mode fiber amplifier

    Page(s): 651 - 656
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    The gain, saturation power, and noise of an erbium-doped single-mode traveling-wave fiber amplifier operating at a wavelength lambda =1.53 mu m are characterized. In continuous-wave (CW) measurements amplification at 2 Gbit/s was demonstrated with up to 17-dB gain for 1*10/sup -9/ bit error rate at 1.531 mu m and a 3-dB full bandwidth of 14 nm. From the determination of the fiber-amplifier's output signal-to-noise ratio versus input signal power during data transmission, it was concluded that, with signal levels used here, signal-spontaneous beat noise limited the receiver sensitivity improvement. With the fiber amplifier acting as an optical preamplifier of the receiver, the best sensitivity was -30 dBm, obtained after installing a polarizer at the fiber amplifier output to reject half of the applied spontaneous emission power. This sensitivity was 6 dB better than without the fiber amplifier, proving that the fiber amplifier can be used as a preamplifier.<> View full abstract»

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  • Noise caused by semiconductor lasers in high-speed fiber-optic links

    Page(s): 657 - 665
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    Theoretical and experimental results are presented for the signal-to-noise (S/N) ratio caused by mode partition noise, intensity noise, and reflection-induced noise in optical data links. Under given conditions an additional noise source with a S/N ratio of 20 dB will cause a power penalty of 1 dB in order to maintain a 10/sup -9/ bit error rate. From numerical simulations the authors predict the maximum allowable dispersion in the presence of mode partition noise to be approximately 40% of a clock period. This figure is almost independent of bit rate and laser structure and agrees well with the measurements and with results of other workers. Numerical simulations of a buried-heterostructure and a TJS laser were carried out at four bit rates from 565 Mbit/s to 4.5 Gbit/s and the measurements were done at 2.2 Gbit/s using a TJS laser.<> View full abstract»

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  • Transmission loss of a 125- mu m diameter PANDA fiber with circular stress-applying parts

    Page(s): 674 - 679
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    The transmission loss of a 125- mu m diameter polarization-maintaining and absorption-reducing optical fiber (the PANDA fiber) with circular stress-applying parts (SAPs) has been investigated. The loss is calculated at a 1.55- mu m wavelength for SAPs consisting of B/sub 2/O/sub 3/ doped silica glasses. The experimental measurements show the validity of the analysis. It is shown that, when the half distance between SAPs is more than 2.2 times the core radius, the additional transmission loss due to B/sub 2/O/sub 3/ absorption is less than 0.05 dB/km with normalized frequency of 2.2 to 2.4 and a B/sub 2/O/sub 3/ dopant concentration of 20 mol.%. As a result, it has been confirmed that transmission losses of 125- mu m diameter PANDA fibers can be comparable to those of commercially available single-mode optical fibers.<> View full abstract»

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  • Doubly coated optical fibres with a low sensitivity to temperature and microbending

    Page(s): 680 - 686
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    In order to prevent microbending losses in optical fibers over a wide temperature range, a new buffer coating and a new top coating have been developed. The buffer coating has a low Young's modulus over a wide temperature range, whereas the top coating has a modulus which is high compared with the modulus of the coatings that are generally used. The application of these coatings results in fibers with a very low microbending sensitivity. However, at low temperatures added optical loss is observed which correlates with a change in the radial stress state of the buffer coating from compression to tension. It is demonstrated by model calculations as well as by experiments that these optical losses can be avoided if the thickness of the buffer layer does not exceed a critical value. The new coatings are shown to provide a good protection of the fiber from mechanical damage.<> View full abstract»

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  • Optical fiber sensor for vibration amplitude measurement

    Page(s): 687 - 691
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (417 KB)  

    An optical fiber vibration sensor capable of measuring vibration amplitudes ranging from 1 mm down to 0.1 mu m with a wide range of frequencies form 0.5 Hz to 100 kHz is described. The proposed method can be used to calibrate accelerometers. In this method the light from a tungsten halogen lamp is made to pass through an optical fiber whose exit end is mounted on the object under test. The emergent light is detected by a lock-in amplifier and then measured by a digital panel meter which can be made to give direct reading of the vibration amplitude. The main advantages of this method are wide dynamic range, wide frequency range, linearity, noise reduction, ruggedness, and light weight. The ultimate detectability can be as much as 0.5 AA/ square root Hz at 1 kHz.<> View full abstract»

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  • Analytical expression for the coupling between two optical fiber cores with alpha -power refractive-index distribution

    Page(s): 694 - 702
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    The authors derive closed-form expression for the coupling coefficient and the butt coupling overlap integral for the coupling between two linearly polarized modes of any order, each propagating an alpha -power refractive-index optical fiber with uniform cladding. To show the usefulness of these formulas, they present numerical results for the coupling between two identical single-mode fibers and clearly demonstrate the variations of the coupling properties as the fiber structure changes. These results are useful when performing coupled-mode analysis of couplers formed between two fibers with the assumed index profiles. The authors also apply the obtained general formulas to evaluating the coupling characteristics between two identical single-mode fibers for various core index distributions.<> View full abstract»

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  • Interferometric chromatic dispersion measurements on short lengths of monomode optical fiber

    Page(s): 703 - 716
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    Chromatic dispersion measurements on short lengths of monomode optical fiber by the technique of 'white light' interferometry are presented. Improved optoelectronic signal processing and rigorous data reduction techniques have resulted in a temporal resolution of >or=7*10/sup -5/ ps.nm/sup -1/ in a 1-m length of fiber, equivalent to 0.06% resolution in the measurement technique. This is equivalent to a first-order chromatic dispersion coefficient (D( lambda )) resolution of 0.07 ps.nm/sup -1/./sup -1/. The second-order chromatic dispersion coefficient (S( lambda )) resolution was 0.02 ps.nm/sup -2/.nm/sup -1/. Experimental results of D( lambda ) and S( lambda ) for three different fibers are compared to theoretical calculation of material and waveguide dispersion.<> View full abstract»

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  • Optical FSK modulation using injection-locked laser diodes

    Page(s): 726 - 728
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    A FSK (frequency shift keying) modulator based on the alpha -parameter induced frequency shift in injection-locked laser diodes is studied. The attainable frequency deviations can easily be set up to several gigahertz by acting on the injected power. A major limitation is found in the switching time which, in some anomalous cases, can become as large as 10 ns.<> View full abstract»

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  • Mode coupling in tapered structures

    Page(s): 729 - 730
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    The theory of strong mode coupling involving nonorthogonal modes is extended to tapered structures. Initially, an attempt is made to show that previous formulations of the problem of nonorthogonal-mode coupling in tapered structures are incomplete. An equation is derived which is the generalization to tapered structures of the coupled-mode formalism with nonorthogonal modes.<> View full abstract»

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  • Orthogonal convolutional coding for the PPM optical channel

    Page(s): 731 - 734
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    Several coding alternatives have been analyzed to improve the performance of the ideal optical pulse position modulation (PPM) optical channel, although it has been shown that performance improvements are difficult to obtain for transmission efficiencies over 1 nat/photon. In the present work, an orthogonal convolutional coding scheme is proposed, achieving better performances than previous coding alternative, over a wide range of efficiencies. Furthermore, a concatenated coding scheme using an orthogonal convolution code as an inner code and a Reed-Solomon code as an outer code is proved to be effective, achieving operation points over 3 nat/photon, with performances that cannot be obtained with other coding schemes.<> View full abstract»

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  • Investigation of Bragg gratings on planar InGaAsP/InP waveguides at normal and oblique incidence

    Page(s): 735 - 739
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    The polarization-dependent mode coupling of Bragg gratings on planar InGaAsP/InP waveguides is investigated by transmittance and reflectance measurements at normal and oblique incidence in the 1.5- mu m wavelength region. Strong coupling between TE (transverse electric) and TM (transverse magnetic) modes is observed at oblique incident, whereas the TE-TE coupling vanishes at an incidence angle of 45 degrees . The behavior of the near field close to the Bragg wavelength and the effects of radiation into the substrate are analyzed. It is experimentally shown that small deformations of the phase fronts on the input side lead to strong interference effects on the output side.<> View full abstract»

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  • Design and performance of nonmetallic waterproof optical fiber cable using water-absorbent polymer

    Page(s): 740 - 746
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    A nonmetallic optical fiber cable waterproofed with absorbent polymer was developed. Methods are proposed for evaluating the reliability of absorbent polymer in order to apply it as a waterproofing material, and a type of polyacrylic acid is selected. In addition, a waterproofing design is established based on a theoretical estimate of the water penetration length in the cable space. Among other findings, it was shown that the optical fiber loss of water-penetrated cable increases due to freezing. The allowable penetration length of waterproof cables can be determined so as to suppress this loss increase. Cables manufactured using this new design and absorbent polymer showed performance sufficient for practical application.<> View full abstract»

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  • Reflection suppression by orthogonal modes

    Page(s): 692 - 693
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    A method is proposed where isolation of a single-frequency laser from reflections of an optical network is obtained using reciprocal elements throughout. The principle is based on the isolation obtained by a double transit quarter-wave plate, which can be generalized. Only linearity and time invariance are required. Thus the network elements can even be nonreciprocal. An application is the isolation of the local-oscillator laser in an integrated optical heterodyne/homodyne receiver View full abstract»

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  • Tunable acoustooptic reflection filters in LiNbO3 without a Doppler shift

    Page(s): 625 - 631
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    A proposal is presented for an acoustooptic filter in LiNbO3 without the Doppler shift, which is normally present in acoustooptic filters and which is undesirable as an intracavity element. This tunable filter has a significantly wider tuning range than previously demonstrated electrooptic filters. A structure incorporating an interdigital acoustic transducer, polarization filter, and single-mode optical waveguide is shown. The design presented works by cascading two acoustooptic filters with an intermediate polarizer, where the Doppler shift experienced in the first filter is precisely compensated for in the second filter. Hence, the output light of the two cascaded acoustooptic filters is not shifted in frequency, thus making the device suitable for applications inside a laser cavity. The filter with intermediate polarizer can be integrated with a single-mode waveguide and requires only a single interdigital acoustic transducer. Crystal symmetry and acoustic power considerations are treated in detail View full abstract»

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  • Comment, with reply, on `Using spread-spectrum in a high-capacity fibre optic local network' by G.J. Foschini and G. Vannucci

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    Among the practical problems mentioned as outstanding by G.J. Foschini and G. Vannucci (see ibid., vol. Lt-6, no.3, p.370-9, 1988) is that of optical power level uniformity requirements. Foschini and Vannucci suggest that this should not be an insurmountable problem, but the commentor claims there is important source of nonuniformity which they appear to have overlooked. In the discussion of star networks, the commenter argues that they dismiss the losses in the coupler as a mathematical inconvenience that would cancel in performance analyses. The commenter aims to show that this is not generally true. In replying, Foschini and Vannucci take issue with the commentor's arguments and with the conclusions of D.B. Mortimore (1985), which serve as the basis of the commentor's arguments View full abstract»

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  • Multibranch frequency-selective reflectors and application to tunable single-mode semiconductor lasers

    Page(s): 666 - 673
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    Multibranch reflectors (MBRs) are proposed as a flexible wavelength-selective element for optical integrated circuits generally and for tunable single-mode lasers specifically. The undesired recurring peaks of reflectivity obtained with two-branch MBRs are spread out in the spectrum by using three or more branches. Design relations are given for the lengths of an arbitrary number of branches, for the selectivity near the peak response, for the wavelength interval to the nearest undesired peak, and for tuning changes in the various branches. It is shown that an MBR is not sensitive to amplitude differences of the order of 20% between the branches, but requires phase control in order to achieve tuning to a specific wavelength. The effects of semiconductor gain variation with wavelength are obtained from a rate-equation solution including MBR. By changing the semiconductor temperature (gain peak) at the same time as the MBR is tuned, a broad range of tuning without jumps is achievable View full abstract»

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  • Time dynamics of outage of fiber optic local system employing spread spectrum

    Page(s): 640 - 650
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    A model is developed for ascertaining the robustness of operation of the random-carrier-code-division multiple-access (RC-CDMA) method of implementing optical frequency division multiple access. The unwanted wander (i.e. the supersensitivity of carrier frequencies to physical perturbations) of each channel is parameterized by σ, of dimensions gigahertz per square root second. Channel outage comes about when, by chance, too many channels crowd into the same part of the optical band, causing overwhelming adjacent channel interference. In this study a lower bound is derived on the mean time between outages (units of years), as a function of bit rate (~10 Mbit/s), chip rate (units of gigabits per second), required signal-to-interference-ratio (~3-30 dB), population size (on the order of ten thousand), and σ. While the technology has not matured to give a clear prognosis of the ability to limit σ, the `payoff', in terms of performance for a given σ, is discussed. Constraints on σ are found that, if met, imply that RC-CDMA can be used to achieve networks with throughput exceeding 100 Gbit/s View full abstract»

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  • TM waves in nonlinear saturable thin films: a multilayered approach

    Page(s): 717 - 725
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    The dispersion of guided TM (transverse magnetic)-polarized waves in a thin nonlinear saturable film bounded by linear media is investigated. The film is assumed to be isotropic with both of the electric field components contributing to its dielectric function. The variation of the wave effective index with the guided power and also with the surface magnetic field intensity is obtained. Different mechanisms giving rise to the nonlinearity of the film are shown to result only in small quantitative differences in the dispersion behavior. A recursive scheme for solving the nonlinear wave equation within the film is fully described. The scheme relates to the saturable dielectric function used and its based on the stratification of the film region into a large number of linear sublayers View full abstract»

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  • Loss factors analysis for single-mode fiber splicing without care axis alignment

    Page(s): 577 - 583
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    Splice loss factors of single-mode fiber splicing lacking core axis alignment were analyzed quantitatively. The optimum splice conditions were also investigated in detail. It was seen that the dominant splice signal-loss factors are core deformation caused by fiber axis discrepancy and core axis misalignment caused by core eccentricity. To suppress average splice loss to less than 0.1 dB, average core eccentricity suppression to less than 0.35 μm is necessary. A novel method for setting fiber endface gaps accurately and quickly is proposed that helps to realize the optimum condition. This method is based on fiber endface image detection using photodiodes, and it has a quick setting time of 5 s and a high accuracy with a setting error of 0.5 μm. A fusion splice machine manufactured based on the present endface setting method was developed and evaluated. As a result, an average splice loss of 0.012 dB was successfully achieved 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