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Lightwave Technology, Journal of

Issue 4 • Date Apr 1991

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Displaying Results 1 - 20 of 20
  • Fiber-embedded in-line isolator

    Publication Year: 1991 , Page(s): 430 - 435
    Cited by:  Papers (6)  |  Patents (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (584 KB)  

    A fiber-embedded optical isolator with a low forward loss has been developed. The isolator consists of thermally diffused expanded core fibers, laminated polarizers, and a Faraday rotation garnet. Backward and forward losses at 1.3 μm wavelength are 44.0 and 0.9 dB, respectively. The isolator has a minute size, and its alignment is simple View full abstract»

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  • Time-resolving wavelength chirp with Fabry-Perot etalons and gratings: a theoretical approach

    Publication Year: 1991 , Page(s): 436 - 441
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (504 KB)  

    Basic dynamic properties of Fabry-Perot (FP) etalons and gratings are investigated for a square-wave shaped input pulse with a linearly changing wavelength. It is shown that for the chirp rates present in distributed feedback (DFB) laser pulses a simultaneous good resolution in the wavelength and time domain is attainable with an etalon due to its small FWHM time-bandwidth product of 0.11. This is not possible with the grating, which has a time∞bandwidth product of 0.89. A simulation of time resolving the dynamic chirp of a DFB laser pulse is presented. The result is compared to the actually calculated incident wavelength variation. The dynamic aspects of FP etalons and gratings for time resolving the wavelength chirp in laser pulses are given View full abstract»

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  • Influence of external mirror on modal behavior of twin-stripe index-guided injection lasers

    Publication Year: 1991 , Page(s): 531 - 534
    Cited by:  Papers (1)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (280 KB)  

    The coupled-mode theory of parallel waveguides is used to calculate the influence of an external mirror on the modal behavior of the AR-coated laser array. The case of twin-stripe index-guided injection lasers with separate contacts is treated in detail. It is shown that for asymmetrical current injection, the external cavity couples the laser's guided array modes and creates new laser-cavity modes with a better mode discrimination in favour of the one having a single far-field pattern. These results imply that multiple laser arrays might benefit from an additional external mirror View full abstract»

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  • Relaxed-tolerance optoelectronic device packaging

    Publication Year: 1991 , Page(s): 477 - 484
    Cited by:  Papers (9)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (840 KB)  

    The authors present an approach to single-mode fiber coupling which results in relaxed alignment tolerances during the package assembly process. The authors use a ball lens to couple from the optical device either directly to single-mode fiber (SMF), or indirectly to SMF through a fiber lens. The ball lens is aligned and mounted in the first assembly stage. The lens is aligned and fixed either mechanically or semiactively. In the second stage of assembly, the SMF is aligned so as to compensate for any small misalignments of the ball lens. The authors have achieved coupling efficiencies of 33-40 % with this coupling scheme. It has been used for coupling to standard laser diodes and to near-traveling wave optical amplifiers. Fiber-to-fiber gains of 8.5-10 dB have been achieved with packaged devices. The approach provides some versatility with respect to the placement of passive optical components inside the package View full abstract»

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  • Passive-quadrature demodulated localized-Michelson fiber-optic strain sensor embedded in composite materials

    Publication Year: 1991 , Page(s): 535 - 544
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1012 KB)  

    A strain sensor embedded in composite materials that is intrinsic, all fiber, local, and phase demodulated is described. It is the combination of these necessary elements that represents an advance in the state of the art. Sensor localization is achieved by using a pair of mirror-ended optical fibers of different lengths that are mechanically coupled up until the desired gauge length for common-mode suppression has been reached. This fiber-optic sensor has been embedded in both thermoset (Kevlar/epoxy and graphite/epoxy) and thermoplastic (graphite/PEEK) composite materials in order to make local strain measurements at the laminar level. The all-fibre system uses a 3×3 coupler for phase demodulation. Parameters such as strain sensitivity, transverse strain sensitivity, failure strain, and frequency response are discussed, along with applications View full abstract»

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  • 1/f frequency noise effects on self-heterodyne linewidth measurements

    Publication Year: 1991 , Page(s): 485 - 493
    Cited by:  Papers (41)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (664 KB)  

    The effects of a 1/f frequency noise on self-heterodyne detection are described, and the results are applied to the problem of laser diode linewidth measurement. The self-heterodyne autocorrelation function and power spectrum are evaluated for both the white and the 1/ f components of the frequency noise. From numerical analysis, the power spectrum resulting from the 1/f frequency noise is shown to be approximately Gaussian, and an empirical expression is given for its linewidth. These results are applied to the problem of self-heterodyne linewidth measurements for coherent optical communications, and the amount of broadening due to 1/f frequency noise is predicted View full abstract»

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  • Theory of an efficient N×N passive optical star coupler

    Publication Year: 1991 , Page(s): 448 - 455
    Cited by:  Papers (8)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (520 KB)  

    A method for configuring an efficient N×N optical passive star coupler is introduced. It makes the construction of a one-piece coupler possible and thus eliminates the excess loss problem associated with cascade couplers and reduces the structural complexity. The authors show that a 100% efficiency figure can be achieved through the entire array by using a properly designed space-varying refractive-index slab. The authors give a mathematical analysis of the space-varying refractive-index slab and examine spatial frequencies of the required refractive-index pattern. The authors demonstrate how the wave-mixing method can be utilized as one possible method of configuring such a slab, using a constant temporal optical frequency involving nonlinear media such as photorefractive crystals View full abstract»

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  • A light intensity function suitable for multimode fiber-optic sensors

    Publication Year: 1991 , Page(s): 545 - 551
    Cited by:  Papers (4)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (536 KB)  

    Intensity distribution functions on the image plane are derived under the assumption that a multimode optic fiber is illuminated by a light source which can be approximated by infinite uniangular beams carrying equal power. The application of the theory to a Lambertian source is discussed. Experimental results, based on the observation of the light intensity distribution imaged on an opaque screen and collected by a digital camera, are presented. The theoretical and experimental data are compared to verify that the intensity function is an accurate model for describing the realistic approach to sensor design. The limitations of the uniangular and uniform intensity distribution models are discussed on the basis of theoretical and experimental results View full abstract»

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  • A new method for electrical frequency locking of optical FDM transmitters

    Publication Year: 1991 , Page(s): 494 - 504
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (864 KB)  

    A novel method for locking the frequency spacing between semiconductor lasers electrically is presented. The method is a modification of the offset frequency master-slave principle. The method allows the frequency spacing between optical channels to be chosen independently, with an accuracy determined by the selectivity of the electronics, and it improves the frequency stability of the locked lasers. A rigorous analytical model of the locking configuration is presented. This model is used to investigate how laser frequency noise and electrical noise from the locking circuit affect the frequency stability of the locked lasers. It is found that the improvements in frequency stability can be achieved for up to 350 lasers, each having a linewidth of 1 MHz. Consequently, the method is suited to lock the transmitters in a coherent optical FDM system View full abstract»

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  • High-isolation polarization-independent optical circulator coupled with single-mode fibers

    Publication Year: 1991 , Page(s): 456 - 460
    Cited by:  Papers (6)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (456 KB)  

    A high-isolation polarization-independent optical circulator is reported. The goal is to provide a simple structure that sharply diminishes the degradation on the isolation caused by imperfection of polarization separation in the polarizing beam splitters. The circulator structure is almost the same as that of a conventional circulator except that a birefringent plate is added to each port to achieve high isolation. The effectiveness of the added birefringent plate has been confirmed by calculation and experiment. Insertion loss and isolation of the fabricated circulator coupled with single-mode fibers have been measured to be <1.0 dB and >29.9 dB, respectively, for 1.299 μm wavelength light. A loss ratio over 28.9 dB has been realized View full abstract»

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  • Polarization independent narrow channel wavelength division multiplexing fiber couplers for 1.55 μm

    Publication Year: 1991 , Page(s): 442 - 447
    Cited by:  Papers (10)  |  Patents (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (568 KB)  

    A polarization-independent narrow-channel (PINC) wavelength division multiplexing (WDM) coupler for operation at 1.55 μm has been designed based on the birefringent properties of fused single-mode couplers. These couplers are made from both conventional single-mode fiber (SMF) and dispersion shifted fiber (DSF). The couplers are designed so that the coupling-coefficient-length products for the two orthogonal polarizations are π out of phase. As a result of the long coupling lengths required, these couplers have very small cross-sectional dimensions, typically on the order of 10 μm View full abstract»

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  • Calculation of bit-error probability for a lightwave system with optical amplifiers and post-detection Gaussian noise

    Publication Year: 1991 , Page(s): 505 - 513
    Cited by:  Papers (60)  |  Patents (29)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (656 KB)  

    The author's previously published results (ibid., vol.8, p.1816-23, 1990) which dealt with the bit-error probability of a lightwave communication system whose noise contribution was exclusively attributed to spontaneous emission noise of optical amplifiers are extended. The earlier theory was based on an NRZ (nonreturn-to-zero) modulation format with zero signal power assigned to logical zeros. The extension is based on the same mathematical technique but includes Gaussian noise originating after the signal has been converted to an electrical current. This noise could be thermal noise, shot noise, or a combination of both. It is no longer assumed that the pulse representing a logical one fills its time slot completely. Now, the optical pulses can be much shorter than the bit period (solitons), the power level of logical zeros need not vanish, and the thermal noise of the postdetection electronic circuit is taken into account View full abstract»

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  • Nonlinear Kerr interactions between modulated waves propagating in a single-mode fiber

    Publication Year: 1991 , Page(s): 422 - 425
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (340 KB)  

    The interactions induced by the nonlinear refractive index in a single-mode optical fiber (Kerr effect) between a modulated wave and a carrier wave have been investigated for amplitude shift keying (ASK), frequency shift keying (FSK), and phase shift keying (PSK). The theoretical analysis, based on a time-domain solution, exploits the well-known formalism of self-phase modulation to describe the propagation of the input electric field in the fiber. The theoretical results were validated experimentally for amplitude- and phase-modulated waves with heterodyne detection techniques. These experiments mimic a coherent transmission system and allow the measurement of the spectrum of each of the waves that participate in the nonlinear interaction View full abstract»

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  • Full-wave analysis of traveling-wave electrodes with finite thickness for electro-optic modulators by the method of lines

    Publication Year: 1991 , Page(s): 461 - 467
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (508 KB)  

    In order to optimize broadband electrooptic modulators with traveling-wave electrodes, detailed information about the propagation constant, the field distribution, and the wave impedance of the modulating field is needed. To get accurate results for these characteristic values, the numerically efficient method of lines (MoL) is used. The MoL takes advantage of the planar structure by discretizing the wave equation in the directions parallel to the metallization plane, whereas an analytical formulation is retained for the transverse direction. Thus, not only the hybrid character of the modulating field but also the finite conductor thickness and anisotropy of the substrate are taken into account. Results for asymmetric coplanar stripline electrodes with typical dimensions on SiO2 buffered LiNbO3 are presented View full abstract»

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  • A novel multilevel coherent optical system: 4-quadrature signaling

    Publication Year: 1991 , Page(s): 514 - 523
    Cited by:  Papers (19)  |  Patents (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (788 KB)  

    A novel multilevel coherent optical system is proposed. It is based on the exploitation of the property that the electromagnetic field propagating in a single-mode optical fiber can be represented by a four-dimensional vector whose components are the phase and quadrature terms of the two polarization components of the electrical field. This allows a wider use of the resources of the electromagnetic field for information transmission in order to obtain a spectrally efficient modulation format with a limited end. The net performance gain with respect to multilevel amplitude and phase modulation (N-APK) and N-PSK increases with an increase in the number of levels N. For instance, for N=32 the gain is 1.6 and 7.7 dB with respect to N-APK and N-PSK systems. The effect of laser phase noise on the system performance is evaluated View full abstract»

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  • Heterodyne video distribution systems sharing transmitter and local oscillator lasers

    Publication Year: 1991 , Page(s): 524 - 530
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (624 KB)  

    The authors present theoretical and experimental results for coherent subcarrier multiplexed (SCM) systems using a novel architecture that shares both the transmitter and local oscillator (LO) laser among multiple optoelectronic receivers. The ability to share both lasers significantly reduces the cost and complexity compared to a multichannel coherent frequency division multiplexed (FDM) system. Experimental results confirm that the system performance can be greatly enhanced by inserting an inline optical amplifier so that many receivers can share one transmitter and LO laser. For example, with an amplifier chip gain of 24 dB, increasing the optical power at the input to the amplifier by 3 dB from -27.6 to -24.5 dBm, the number of receivers can be increased from 2 to 32 View full abstract»

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  • Microwave modulation of laser diodes with optical feedback

    Publication Year: 1991 , Page(s): 468 - 476
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (572 KB)  

    It is shown theoretically and experimentally that significant variations in the microwave modulation responses of laser diodes occur due to optical feedback from the transmission fiber. These variations decrease if the laser spectrum is less coherent; this can be achieved, for example, by increasing the intensity modulation index. In a recent letter the authors (1989) discussed the small-signal transfer functions; large deviations in the amplitude and the phase response resulted from optical feedback. For large-signal modulation, weaker feedback-induced deviations of the transfer function were predicted by W.I. Way and M.M. Choy (1988). The microwave modulation characteristics are considered in more detail, including the effects of higher modulation indexes. For a typical intensity modulation index of 26%, variations of up to 3 dB in amplitude and 60° in phase were observed View full abstract»

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  • Strength improvement and fusion splicing for carbon-coated optical fiber

    Publication Year: 1991 , Page(s): 417 - 421
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (476 KB)  

    Problems associated with the use of carbon coating on silica fibers, including the initial strength and fusion splicing, were examined. A carbon-coated fiber with 6.2-kgf failure strength and excellent hydrogen resistance was obtained by suppressing strength degradation due to carbon coating. A scanning microscope utilized to estimate the carbon surface roughness and a smooth surface was found to be essential to obtain high strength. These results show that no significant technical problems remain for carbon-coated fiber and that it is now ready for practical application View full abstract»

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  • Transmission characteristics of optical asymmetric Y junction with a gap region

    Publication Year: 1991 , Page(s): 426 - 429
    Cited by:  Papers (5)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (276 KB)  

    A novel type of asymmetric Y junction structure is proposed. This Y junction has a gap region so that the required power splitting ratio can be obtained simply even when the branching angle is kept fixed. The transmission characteristics of the proposed Y junction are simulated by means of a beam propagation method (BPM). It is shown that this Y junction has a marked advantage of flexibility in practical use over the conventional asymmetric Y junction. It is estimated that, when the configuration is applied to the 3-dB power divider, a drastic reduction in radiation losses compared with usual symmetric Y junction results View full abstract»

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  • Fiber-optic sensor using an injection-locked local laser

    Publication Year: 1991 , Page(s): 552 - 557
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (564 KB)  

    An interferometric fiber-optic sensor using a local laser is proposed. An Er-doped-fiber ring-laser is injection locked to a signal carrier using a fiber coupler, and the extracted carrier is directly homodyned with the signal light at the output of the coupler. With a feedback loop suppressing the local laser instability, demodulation linearity over two decades and minimum detection in the 10-3 rad range are attained. The Er-doped fiber ring laser constructed for this work has a linewidth of less than 1.4 kHz. Acceptable signal frequency ranges and the linearity and sensitivity of the proposed sensor are examined. Also discussed is the applicability of this configuration to simple, long-spanned sensors 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