By Topic

Lightwave Technology, Journal of

Issue 5 • Date May 1995

Filter Results

Displaying Results 1 - 25 of 29
  • Circulating loop transmission experiments for the study of long-haul transmission systems using erbium-doped fiber amplifiers

    Page(s): 879 - 888
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (824 KB)  

    A circulating loop transmission experiment is a useful tool for the research and development of long-haul transmission systems that use erbium-doped fiber-amplifier repeaters. Circulating loop techniques, applied to an amplifier chain of modest length, can provide an experimental platform to study a broad range of transmission phenomena for EDFA-based transmission systems. A loop experiment attempts to simulate the transmission performance of a multi-thousand kilometer long system by reusing or recirculating an optical signal through a modest length amplifier chain of tens to hundreds of kilometers. This paper reviews original loop techniques developed to study various parameters of long-haul transmission using erbium-doped fiber-amplifiers repeaters for undersea systems. Transmission experiments were performed at transoceanic distances with 33 and 46 km amplifier spacing, operating at 5 and 10 Gb/s. Experimental data is provided here for various parameters, including bit error ratio, Q-factor, and spectral broadening View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • WDM systems with unequally spaced channels

    Page(s): 889 - 897
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (844 KB)  

    Crosstalk due to four-wave mixing (FWM) is the dominant nonlinear effect in long-haul multichannel optical communication systems employing dispersion-shifted fiber. A method is discussed to find non-uniform channel separations for which no four-wave mixing product is superimposed on any of the transmitted channels, therefore suppressing FWM crosstalk. The residual crosstalk, due to channel power depletion only, is analytically evaluated for intensity-modulated repeaterless wavelength-division-multiplexed (WDM) systems and compared to experimental results. The theory includes the effect of the channel depletion on the amplitude of each phase-matched FWM wave. The probability of error is evaluated including the statistics of the pattern dependent channel depletion. The BER curve computed for an 8-channel WDM system is found to be in good agreement with experimental results. In the experiment, repeaterless transmission of eight 10 Gb/s WDM channels over 137 km (11 Tb/s-km) of dispersion-shifted fiber was demonstrated and error-free operation was achieved over a wide range of input powers using unequally spaced channels. The same system with equally spaced channels could not achieve a probability of error lower than 10-6. The use of unequal channel spacing allowed fiber input power to be increased by as much as 7 dB, which could be translated into a fivefold increase of the bit rate per channel (and therefore of the system capacity), or to an increase in the system length of about 30 km View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Performance analysis of self-synchronized optically preamplified PPM

    Page(s): 923 - 932
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (736 KB)  

    The performance of a hybrid erbium-doped fiber amplifier pulse position modulation (EDFA PPM) system is investigated under self-synchronization. Sensitivity results are presented for a system operating at 622 Mb/s and λ=1.53 μm. These indicate that EDFA PPM offers 7.9 dB sensitivity improvement over an equivalent EDFA PCM system and is beyond the fundamental PCM limit. An original expression is derived for the EDFA PPM power spectral density (PSD) under jitter. Original results are presented for the timing variance and the jitter wrong slot error (JWSE) probability due to the extracted self-timing. An original analysis and results are given for the system sensitivity penalty due to jitter. The penalty varied between 0.15 and 1.9 dB for the range of parameters considered. The selection of the system parameters that minimizes the penalty is investigated View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Calculating the performance of optical CPFSK phase diversity receivers

    Page(s): 971 - 976
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (344 KB)  

    Numerical method for efficiently computing the performance of continuous phase frequency shift keying (CPFSK) is presented. The receiver uses a phase diversity technique with a delay-and-multiply frequency discriminator to recover the phase of the optical signal. The moment generating function (MGF) of the discriminator is derived and used in the calculation of bit error rate (BER). The results of numerical integration show that the receiver output is far from Gaussian. Exact mean and variance are derived for the Gaussian approximation (GA). The effects of laser linewidth, filter bandwidth, and shot noise correlation are all considered View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Performance limitations imposed on all-optical ultralong lightwave systems at the zero-dispersion wavelength

    Page(s): 898 - 905
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (724 KB)  

    The performance limitations imposed on all-optical transoceanic lightwave systems are discussed. Specifically, the performance of a 8910-km-long 5-Gb/s communication system with in-line optical amplifiers is evaluated. The analysis, which is performed both analytically and with the aid of computer simulations, considers the impact of the transmission impairments on the system performance. In particular, the impairments due to the accumulated amplified spontaneous emission noise, the fiber dispersion, the fiber nonlinearity and polarization effects are analyzed, and improvement methods are suggested View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Optimal spectral and power parameters for all-optical wavelength shifting: single stage, fanout, and cascadability

    Page(s): 771 - 781
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (908 KB)  

    We analyze a gain-saturated semiconductor-optical-amplifier (SOA) all-optical wavelength shifter with respect to its spectral and power characteristics as well as its capability for high fanout and cascadability. The extinction and signal-to-noise ratios, the two main figures-of-merit for a wavelength-shifted signal, are determined by accounting for gain saturation and spectral shifting which occur due to the depletion of the injected carrier density View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Limitations imposed by polarization-dependent gain and loss on all-optical ultralong communication systems

    Page(s): 906 - 913
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (716 KB)  

    The performance degradation of an all-optical ultralong system due to polarization dependent loss and polarization dependent gain is analytically analyzed. In particular, both the mean and the standard deviation of the performance are calculated. The analytical predictions are compared against a computer simulator, which includes the effects of nonlinearity and polarization mode dispersion. The result show that polarization dependent gain is the major source of degradation for the mean performance, while both polarization dependent loss and gain affect the standard deviation from the mean performance. Finally, the performance improvement due to polarization scrambling is evaluated View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Rayleigh backscatter effects on 1550-nm CATV distribution systems employing optical amplifiers

    Page(s): 933 - 946
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1068 KB)  

    We analyzed the applicability of externally modulated 1550-nm laser transmitters for trunking and distribution of AM CATV channels using power and in-line EDFA's. The distribution of multiple AM CATV channels over long fiber spans is degraded by the presence of Rayleigh backscatter-induced low-frequency interferometric noise. When the laser source is modulated externally, the low-frequency interferometric noise is mixed and translated around the AM carriers. Furthermore, when isolators are not used with the optical amplifiers, the low end of the broadcast channels could be severely degraded due to doubly amplified Rayleigh backscatter. Employing narrow-linewidth semiconductor or Nd:YAG laser sources at the transmitter will lower the tail of the low-frequency interferometric noise level but will increase the translated noise peak level at each AM carrier. Therefore, the standard CNR measurement techniques, which assumes the noise spectrum is flat, may not reveal the correct video picture quality seen at the customer premises. In this analysis, we compared NCTA RF CNR and baseband video SNR results using CCIR recommended unified weighting filter. We determined that for laser linewidth less than 1 MHz and with long fiber spans, baseband video SNR as opposed to RF CNR measurements should be used to characterize the performance of AM-VSB CATV broadcast distribution systems. Finally, an experimental 78-channel AM-VSB CATV distribution system is constructed employing two EDFA's simulating head-end and hub sites and we compared RF CNR and baseband video SNR measurements using a 700-kHz linewidth externally modulated 1550-nm DFB transmitter View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Mid-range coherent optical frequency domain reflectometry with a DFB laser diode coupled to an external cavity

    Page(s): 954 - 960
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (592 KB)  

    The optical frequency of an external double cavity coupled laser diode was controlled via the phase of the feedback light. Strong linewidth and mode hopping reductions were obtained, extending coherent reflectometry with semiconductor sources to the range of hundreds of meters View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Recent progress in amplified undersea systems

    Page(s): 829 - 840
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1080 KB)  

    The advent of the optical amplifiers has removed the loss limitation of the fiber in the conventional undersea systems using 3R (retiming, reshaping, regenerating) repeaters, and it has introduced new design criteria for the undersea lightwave systems. The accumulation of the small impairment factors that was negligible in the conventional system becomes significant to determine the transmission performances of the amplified system. The fiber nonlinearity is a distinctive limitation factor that dominates the transmission performance of the amplified system, although it was not a limitation factor in the conventional system. This paper describes the recent progress of the undersea lightwave cable systems employing optical amplifier repeaters. The limitation factors and the polarization dependent characteristics of the amplified system are described. The system demonstrations with conventional IM-DD technology are presented using both recirculating loop and straight fiber transmission line. The system maintenance method is also explained briefly. Future technologies adopting the WDM or the optical solitons are also discussed View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Multi-stage erbium-doped fiber amplifier designs

    Page(s): 703 - 720
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1736 KB)  

    Applications for erbium-doped fiber optical amplifiers have been multiplying in recent years, and increasingly complex structures have been introduced. We review characteristics and design parameters, the use of interstage elements, and various digital transmissions systems applications for multi-stage amplifiers. A notation is introduced to describe multi-stage fiber amplifiers View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Detailed noise statistics for an optically preamplified direct detection receiver

    Page(s): 977 - 981
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (416 KB)  

    We describe the exact statistics of an optically preamplified direct detection receiver by means of the moment generating function. The theory allows an arbitrary shaped electrical filter in the receiver circuit. The moment generating function (MGF) allows for a precise calculation of the error rate by using the inverse Fast Fourier transform (FFT). The exact results are compared with the usual Gaussian approximation (GA), the saddlepoint approximation (SAP) and the modified Chernoff bound (MCB). This comparison shows that the noise is not Gaussian distributed for all values of the optical amplifier gain. In the region from 20-30 dB gain, calculations show that the GA underestimates the receiver sensitivity while the SAP is very close to the results of our exact model. Using the MGF derived in the article we then find the optimal bandwidth of the electrical filter in the receiver circuit and calculate the sensitivity degradation due to inter symbol interference (ISI) View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Reduction of Gordon-Haus jitter in soliton transmission systems by optical phase conjugation

    Page(s): 850 - 855
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (484 KB)  

    The effect of optical phase conjugation on Gordon-Haus jitter in long-distance soliton communication systems is considered. In-line optical phase conjugation at an optimal point two-thirds of the way down the system reduces the rms jitter by a factor of three. A post-transmission-line compensation scheme based on optical phase conjugation and soliton-supported dispersion compensation reduces the rms jitter by a factor of two View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Inhomogeneously broadened fiber-amplifier cascades for transparent multiwavelength lightwave networks

    Page(s): 782 - 790
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (712 KB)  

    The emergence of practical fiber-amplifier chains has swiftly raised the prospect of transparent lightwave networks, in which signals travel from source to destination through a sequence of intermediate nodes without optoelectronic conversion. When such networks employ multiple wavelengths, however, some of the most substantial new research challenges are those posed by the amplifier chains themselves. Such networks suffer from accumulating interchannel power spread, from sensitivity to interamplifier loss variations, and from transient cross saturation, as the network undergoes reconfiguration. All of these difficulties effectively vanish in a chain of saturated lightwave amplifiers whose per-channel gains are decoupled by, e.g., inhomogeneous broadening. Unlike conventional, homogeneously broadened systems, saturated fiber-amplifier chains with decoupled gain dynamics provide automatic channel-by-channel power regulation, tolerance to interamplifier loss variations, and immunity to transient cross saturation. Thus, if amplifiers with such decoupled gain dynamics can be implemented in a practical way, they promise to solve-in a single stroke-several of the most substantial technological challenges facing transparent multiwavelength lightwave networks View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Transmission of many WDM channels through a cascade of EDFA's in long-distance links and ring networks

    Page(s): 802 - 816
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1244 KB)  

    We analyze the transmission of many wavelength-division-multiplexed (WDM) channels through a cascade of erbium-doped fiber amplifiers (EDFA) in both long-distance links and ring-based networks. For a megameter long-distance system, optimal operating conditions are found for achieving a high signal-to-noise ratio (SNR) per channel with as small an SNR differential as possible between 20 WDM channels spaced 0.5 nm apart. Critical issues addressed in this paper include: (a) the non-uniformity of the EDFA gain with wavelength: (b) the link loss between amplifiers; (c) the small-signal gain per amplifier; and (d) the input signal power View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Bit-dependent degradation caused by stimulated Brillouin scattering in CPFSK coherent optical repeaterless systems with booster amplifiers

    Page(s): 914 - 922
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (668 KB)  

    An interesting phenomenon due to stimulated Brillouin scattering (SBS) is experimentally found in a CPFSK heterodyne system with a booster amplifier. We find that the demodulated waveform amplitudes of just a few distinguished bits are strongly suppressed leading to a significant increase in BER. It is confirmed that the BER degradation can be reduced by adjusting the threshold voltage bias of the receiver decision circuit View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Uniform 8×8 lithium niobate switch arrays

    Page(s): 967 - 970
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (348 KB)  

    We report the fabrication and characterization of two packaged 8×8 Ti:LiNbO3 switch arrays. The devices, with their polarization-maintaining fiber arrays, exhibit low crosstalk and excellent uniformity in control voltages and insertion loss View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Transmission distance of in-line amplifier systems with group-velocity-dispersion compensation

    Page(s): 862 - 867
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (560 KB)  

    Group-velocity dispersion (GVD) compensation in in-line amplifier systems is evaluated from the viewpoint of improving the transmission distance. The nonlinear Schrodinger equation, which simulates signal propagation in optical fibers, is numerically evaluated to clarify the optimum configuration for GVD compensation. It is shown that the optimum amount of GVD compensation is about 100% of the GVD experienced by the transmitted signal. The optimum compensation interval is found to be a function of the bit rate, signal power, and dispersion parameter. For dispersion parameter values ranging from about -0.1 ps/nm/km to -10 ps/nm/km, and an amplifier noise figure of about 6 dB, the optimum compensation configuration can eliminate the GVD from in-line amplifier systems, thus improving transmission distances to those limited by self-phase modulation and higher-order GVD View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Multi-wavelength all-optical networks with wavelengths outside the erbium-doped fiber amplifier bandwidth

    Page(s): 791 - 801
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (948 KB)  

    Erbium-doped fiber amplifiers have become the dominating technology for signal amplification in all-optical networks. One constraint of EDFA's is that they have a much narrower bandwidth (≈25 nm) compared to the low-loss region (≈200 mn) of optical fiber. Instead of using only wavelengths within the bandwidth of EDFA's (i.e. the inband channels) for communication, we propose to include wavelengths outside the EDFA bandwidth (i.e. the outband channels) as well in order to increase the number of wavelengths and/or channel spacings that can be accommodated. Using outband wavelengths for sending messages presents a new constraint, namely that only if the power loss for transmitting a message is small enough can this message be transmitted on the outband wavelength. We develop wavelength-routing algorithms on arbitrary network topologies and wavelength assignments in hierarchical networks for sending messages subject to this constraint. We also analyze the SNR for inband/outband WDM signals View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Synchronization for passive optical networks

    Page(s): 947 - 953
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (676 KB)  

    There is widespread interest in the passive optical network as a solution for a future fiber in the loop network. This paper addresses the problem of synchronization at the line termination of a passive optical network that uses high-speed time division multiple access. Synchronization is a critical function since each asynchronous transfer mode (ATM) cell arrives with unknown phase. An ASIC has been developed to perform this function at 622 Mb/s and is outlined here View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • An alternative to white light interferometric sensing

    Page(s): 961 - 966
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (520 KB)  

    An optical scanning technique is presented as an alternative to white light interferometry. In this technique, it is possible to eliminate the receiving interferometer used in a conventional two-interferometer white light interferometric system and hence a simple, stable and compact sensor device may be realized. A high resolution and large operating range also becomes possible with this system View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Four-photon mixing and high-speed WDM systems

    Page(s): 841 - 849
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (656 KB)  

    The trend toward higher bit rates in lightwave communications has increased interest in dispersion-shifted fiber to minimize dispersion penalties. At the same time optical amplifiers have increased interest in wavelength multiplexing. These two methods of increasing system capacity, if used together, can result in severe degradation due to fiber nonlinearity. This paper discusses the impact of the principal nonlinearity, four-photon mixing, and describes strategies that allow simultaneous use of high bit rates and WDM View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Erbium-doped-fiber optical limiting amplifiers

    Page(s): 732 - 739
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (560 KB)  

    A novel configuration of an erbium-doped-fiber optical output-limiting amplifier (OLA) is presented which is realized by simply introducing a differential lump-loss between the signal and the pump power at a particular point along the fiber. The OLA exhibits an input-power dynamic range in excess of 40 dB and the capacity to control optically the level of the constant-output signal View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Ultra-high-speed OTDM networks using semiconductor amplifier-based processing nodes

    Page(s): 761 - 770
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (824 KB)  

    The use of semiconductor amplifiers in high speed communications systems is reviewed. Processing of signals at 10 Gb/s in a 40-Gb/s OTDM network is demonstrated using nonlinear loop mirror configurations, and mode locked ring lasers. Particular attention is paid to the role of carrier density modulation, long believed to be a detrimental effect, and its useful exploitation View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A simple expression for optical FDM network scale considering fiber four-wave mixing and optical amplifier noise

    Page(s): 856 - 861
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (424 KB)  

    Possible transmission distance and number of channels are studied in optical FDM (frequency division multiplexed) systems. Optical amplifier noise and fiber four-wave mixing, which respectively restrict input power to a repeater and input power to a fiber, are taken into account. A simple analytical expression is derived for evaluating FDM network scale by using a Gaussian noise approximation. Calculation examples are also presented View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.

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