Showing papers on "Wavelength-division multiplexing published in 2002"

Optical differential quadrature phase-shift key (oDQPSK) for high capacity optical transmission

Abstract: Signaling using oDQPSK offers great potential for application in 10 and 40 Gb/s DWDM transmission systems, offering increased spectral efficiency, relaxed dispersion management and improved PMD tolerance. Practical realization of encoder and decoder functionality through integration should lead to wide system application.

Subcarrier multiplexing for high-speed optical transmission

Abstract: The performance of high-speed digital fiber-optic transmission using subcarrier multiplexing (SCM) is investigated both analytically and numerically. In order to reduce the impact of fiber chromatic dispersion and increase bandwidth efficiency, optical single-sideband (OSSB) modulation was used. Because frequency spacing between adjacent subcarriers can be much narrower than in a conventional DWDM system, nonlinear crosstalk must be considered. Although chromatic dispersion is not a limiting factor in SCM systems because the data rate at each subcarrier is low, polarization mode dispersion (PMD) has a big impact on the system performance if radiofrequency (RE) phase detection is used in the receiver. In order to optimize the system performance, tradeoffs must be made between data rate per subcarrier, levels of modulation, channel spacing between subcarriers, optical power, and modulation indexes. A 10-Gb/s SCM test bed has been set up in which 4 /spl times/ 2.5 Gb/s data streams are combined into one wavelength that occupies a 20-GHz optical bandwidth. OSSB modulation is used in the experiment. The measured results agree well with the analytical prediction.

WDM optical network with passive pass-through at each node

Abstract: A communications network has a plurality of nodes interconnected by an optical transmission medium. The transmission medium is capable of a carrying a plurality of wavelengths organized into bands. A filter at each node for drops a band associated therewith and passively forwards other bands through the transmission medium. A device is provided at each node for adding a band to the transmission medium. Communication can be established directly between a pair of nodes in the network sharing a common band without the active intervention of any intervening node. This allows the network to be protocol independent. Also, the low losses incurred by the passive filters permit relatively long path lengths without optical amplification.

Fault management in IP-over-WDM networks: WDM protection versus IP restoration

Abstract: We consider an IP-over-WDM network in which network nodes employ optical crossconnects and IP routers. Nodes are connected by fibers to form a mesh topology. Any two IP routers in this network can be connected together by an all-optical wavelength-division multiplexing (WDM) channel, called a lightpath, and the collection of lightpaths that are set up form a virtual topology. In this paper, we concentrate on single fiber failures, since they are the predominant form of failures in optical networks. Since each lightpath is expected to operate at a rate of few gigabits per second, a fiber failure can cause a significant loss of bandwidth and revenue. Thus, the network designer must provide a fault-management technique that combats fiber failures. We consider two fault-management techniques in an IP-over-WDM network: (1) provide protection at the WDM layer (i.e., set up a backup lightpath for every primary lightpath) or (2) provide restoration at the IP layer (i.e., overprovision the network so that after a fiber failure, the network should still be able to carry all the traffic it was carrying before the fiber failure). We formulate these fault-management problems mathematically, develop heuristics to find efficient solutions in typical networks, and analyze their characteristics (e.g., maximum guaranteed network capacity in the event of a fiber failure and the recovery time) relative to each other.

Recent advances in high-density and large-scale AWG multi/demultiplexers with higher index-contrast silica-based PLCs

Abstract: This paper reviews recent progress on high-density and large-scale arrayed-waveguide-grating (AWG) multi/demultiplexers, which have been developed for wavelength division multiplexing (WDM)-based photonic networks. The AWG has been the key to the construction of flexible and large-capacity WDM networks. This is because, compared with conventional filters consisting of thin-film interference filters and microoptics, the AWG offers the advantages of low loss, high port counts, and mass productivity. To improve such characteristics further, low-loss, higher index-contrast (super-high /spl Delta/) planar lightwave circuits (PLCs) with a bending radius of 2 mm have recently been developed. It has been shown that these PLCs are effective for use in constructing a compact AWG module with 1/5 the volume of a conventional module and large-scale AWGs with 256 and 400 channels. Three techniques for low-loss fiber connection with spot-size converters have also been developed for the super-high /spl Delta/ PLCs, and it has been confirmed that these techniques can be applied to the fabrication of AWG modules. Furthermore, two-stage tandem AWG-type multi/demultiplexers with more than 1000 channels have been demonstrated. This paper describes the progress that has been made on these high-density and large-scale AWGs, which are expected to contribute greatly to the construction of future photonic networks including optical add/drop multiplexing systems and optical crossconnect systems.

Microdisk tunable resonant filters and switches

Abstract: Tunable, vertically coupled InP microdisk resonant filters having a p-i-n active region and utilizing free carrier injection (FCI) to alter the index of refraction are presented for the first time. The fabricated devices allow single-mode operation and exhibit a large free spectral range (FSR=10 nm) with high Q values of 7000. Tuning of the resonant characteristics by free carrier injection is demonstrated. The resonant wavelengths of the disk cavity blue-shifts at a rate of 1 nm/mA.

MEMS: the path to large optical crossconnects

Abstract: Continuous growth in demand for optical network capacity and the sudden maturation of WDM technologies have fueled the development of long-haul optical network systems that transport tens to hundreds of wavelengths per fiber, with each wavelength modulated at 10 Gb/s or more. Micro-electromechanical systems devices are recognized to be the enabling technologies to build the next-generation cost-effective and reliable high-capacity optical crossconnects. While the promises of automatically reconfigurable networks and bit-rate-independent photonic switching are bright, the endeavor to develop a high-port-count MEMS-based OXC involves overcoming challenges in MEMS design and fabrication, optical packaging, and mirror control. Due to the interdependence of many design parameters, manufacturing tolerances, and performance requirements, careful trade-offs must be made in MEMS device design as well as system design. We provide an overview of the market demand, various design trade-offs, and multidisciplinary system considerations for building reliable and manufacturable large MEMS-based OXCs.

Impact of segments aggregation on TCP Reno flows in optical burst switching networks

Abstract: We study the optical burst switching (OBS) paradigm for the support of the TCP flows in an all optical network (AON). We analyze the TCP send rate, i.e. the amount of data sent per time unit, taking into account of: (i) the burst assembly mechanism, called burstification process; (ii) the burst loss events inside the OBS network. The goals of the paper are to investigate the effect of the variation of the burstification period and to derive some general guidelines about the dimensioning of the burstification period. With respect to the case in which any assembly mechanism is missing, the results show that an accurate dimensioning of the burstification period yields negligible penalties with regard to the low speed sources and significant benefits with regard to the high speed sources.

Performance evaluation of a new technique for IP support in a WDM optical network: optical composite burst switching (OCBS)

Abstract: The optical composite burst switching (OCBS) technique is proposed to be implemented in an all-optical backbone network to support Internet protocol (LP) traffic. The OCBS is based on two main features. First, several IP packets are assembled in a single macropacket, called burst. Second, the burst contention in an optical switch is handled by means of two techniques, the wavelength dimension and the burst-dropping (BD) technique. Different from traditional optical burst switching, where an entire burst is discarded when all of the output wavelengths are engaged at the arrival instant of the burst, a switch adopting the BD technique discards only the initial part of a burst finding all of the engaged output wavelengths while forwarding the final part of the burst, beginning at the instant in which one wavelength becomes free. The OCBS allows an increase in the switch throughput in terms of number of accepted IP packets because a burst contains a given number of IP packets. We introduce the analytical model that allows us to evaluate the effectiveness of the technique and, in particular, the obtained saving; furthermore, a sensitivity analysis of the saving, with respect to both the optical burst switch parameters and the traffic load, is carried out.

Optical Network Survivability: Protection Techniques in the WDM Layer

Abstract: This paper is an introduction to survivability of WDM networks. All the main optical protection techniques proposed as far as now for the WDM layer are classified and reviewed. In particular, commonly adopted protection strategies for ring and mesh networks are explained. Moreover, off-line planning of WDM networks able to support path protection is briefly introduced. Finally, an example of heuristic network-capacity optimization is presented, discussing results obtained by considering a case-study network.

Parallel-cascaded semiconductor microring resonators for high-order and wide-FSR filters

Abstract: We demonstrate an optical channel dropping filter (OCDF) using three parallel-cascaded vertically coupled microrings with improved rolloff, bandpass flattening, and wide free spectral range (FSR) compared to a single-ring OCDF using single-mode tightly confined waveguides in both GaAs-AlGaAs and GaInAsP-InP. We achieve FSRs of 30 nm for GaAs-AlGaAs and 40 nm for GaInAsP-InP devices, which are three and four times greater, respectively, than those for single rings. The rolloff is 2.8 times faster than that for a single ring.

Polarization-independent two-pump fiber optical parametric amplifier

Abstract: Fiber-optical parametric amplifiers can be rendered polarization-independent by using two pumps with orthogonal polarization states. We have analytically investigated and experimentally demonstrated, for the first time to our knowledge, a flat-gain polarization-independent continuous-wave fiber optical parametric amplifier with 15 dB of gain over a 20-nm bandwidth, by using two orthogonal pumps.

Upstream traffic transmitter using injection-locked Fabry-Perot laser diode as modulator for WDM access networks

Abstract: An upstream-traffic transmitter based on a Fabry-Perot laser diode (FP-LD) as modulator is proposed and demonstrated for wavelength division multiplexed (WDM) access networks. By injection-locking the FP-LD with the downstream wavelength at the optical network unit (ONU), the original downstream data can be largely suppressed while the upstream data can be transmitted on the same injection-locked wavelength by simultaneously directly-modulating the FP-LD.

Equalization and FEC techniques for optical transceivers

Abstract: In this tutorial paper, we present the application of well-known DSP techniques used in lower speed wireline and wireless applications, to high-speed optical communications. After an introduction on today's optical network architecture and typical optical channel impairments, we study techniques such as fiber equalization, maximum likelihood detection, and current and next generations Forward Error Correction (FEC), with special emphasis on VLSI implementation.

Optical fiber coupling configurations for a main-remote radio base station and a hybrid radio base station

Abstract: A main-remote radio base station system includes plural remote radio units. Fiber costs are significantly reduced using a single optical fiber that communicates information between the main unit and the remote units connected in a series configuration. Information from the main unit is sent over a first fiber path to the remote units so that the same information is transmitted over the radio interface by the remote units at substantially the same time. The main unit receives the same information from each of the remote units over a second fiber path at substantially the same time. Delay associated with each remote unit is compensated for by advancing a time when information is sent to each remote unit. A data distribution approach over a single fiber avoids the expense of separate fiber couplings between the main unit and each RRU. That approach also avoids the expense of WDM technology including lasers, filters, and OADMs as well as the logistical overhead needed to keep track of different wavelength dependent devices.

Communications network for a metropolitan area

Abstract: A communications network for a metropolitan area is disclosed The network is comprised of three basic types of nodes: an access multiplexer, a photonic switch, and a core node The access multiplexer provides multiplexing of data packets from end-users onto at least one sparse wavelength division multiplexed (SWDM) wavelength The SWDM wavelengths are carried over fiber cable to the photonic switches, which consolidate these wavelengths into dense wavelength division multiplexed (DWDM) wavelengths for transmission to the core node The core nodes include a photonic switch (PSX) and a service-aware terabit router core for routing packets within the metropolitan area via the network or out to a long haul network The photonic switches and core nodes are capable of switching at the wavelength, group of wavelength, and fiber levels

Symmetric highly efficient (/spl sim/0 dB) wavelength conversion based on four-wave mixing in quantum dot optical amplifiers

Abstract: Conversion efficiency to longer wavelengths in four-wave-mixing-based wavelength conversion in optical semiconductor amplifiers is generally much lower than that in the opposite direction. This study demonstrates experimentally that this feature is drastically improved, and the asymmetry between conversion directions is eliminated by using quantum dots in the active layer. We attribute this to a reduction in linewidth enhancement factor due to the discreteness of the electron states in quantum dots.

Method and apparatus for dynamic equalization in wavelength division multiplexing

Abstract: An adjustable diffractive light modulator is used to equalize the power level of wavelength multiplexed signals in wavelength division multiplexing applications. An optical channel transmits a multi-wavelength input signal through a wavelength demultiplexer. The input signal comprises a plurality of component signals defined according to a plurality of wavelengths. The de-multiplexer spatially separates the multi-wavelength input signal into its respective plurality of component signals, which are transmitted through a plurality of optical channels onto a plurality of controllable diffractive light modulators. The diffractive light modulators are advantageously comprised of grating light valves. Component signals are reflected off their respective diffractive light modulators and collected in a plurality of optical channels for re-transmission into a wavelength multiplexer. The reflected signals are combined through a multiplexing process and transmitted as an output beam. Control of the diffractive light modulator is achieved by sensors measuring the power level of signals passing through the plurality of optical channels. The measured power levels of light are converted to digital values which are input into an electronic controller for processing. Control output signals from the controller are used to independently control individual pixels within the diffractive light modulator to equalize the reflected light signals.

Optical transmitter and optical transmission system

Abstract: The present invention suppresses to a minimum the degradation of the transmission quality caused by chromatic dispersion characteristic of an optical transmission medium, and the interplay between the chromatic dispersion and non-linear optical effects in dense WDM transport systems A baseband input data signal is precoded in advance by a pre-coding unit (2), phase modulation is carried out using a precoded signal by the optical phase modulating unit (3), and the phase modulated optical signal is converted to an RZ intensity modulated signal by the optical filter unit (5) that performs phase-shift-keying to amplitude-shift-keying conversion For example, an optical phase modulating unit (3) generates an encoded DPSK phase modulated signal using a differential phase shirt keying (DPSK) format, and a phase modulated signal is converted to an RZ intensity modulated signal by the optical filter unit (5) disposed downstream of the optical phase modulating unit (3)

All-optical signal up-conversion for radio-on-fiber applications using cross-gain modulation in semiconductor optical amplifiers

Abstract: The authors present a novel scheme of up-converting optical intermediate frequency (IF) signals with an optical local oscillator (LO) signal using cross-gain modulation in a semiconductor optical amplifier. This scheme provides high conversion efficiency and is independent of the incident light wavelength and polarization. It can be useful for radio-on-fiber transmission system applications in which one remote LO signal is provided for several wavelength-division-multiplexing IF signals.

Theory of spectral beam combining of fiber lasers

Abstract: We model the spectral beam combining of a fiber laser array in the external resonator configuration, as proposed by V. Daneu et al. A diffraction integral-based approach is used that leads to design principles for most significant measures of performance, such as efficiency, bandwidth, and beam quality. Sensitivity to alignment and positioning errors is also characterized. Off-axis transform lens aberrations are shown to limit array size, and two design criteria are applied to compare the performance of simple spherical, compound, and aspheric lenses. The results indicate that a simple aspheric lens is superior in meeting the proposed criteria to a well-designed compound (quadruplet) lens with spherical surfaces. Application to the efficient coupling of a laser array to a multimode fiber core is discussed as a final example.

Optical filters based on ring resonators with integrated semiconductor optical amplifiers in GaInAsP-InP

Abstract: A key device in all-optical networks is the optical filter. A ring resonator filter with an integrated semiconductor optical amplifier (SOA) on the basis of GaInAsP-InP has been investigated and fabricated. A required passband shape of loss-compensated ring resonator filters can be custom-designed by the use of multiple coupled resonators. Results of single-, double-, and triple-ring resonators with integrated SOAs with free spectral ranges of 12.5, 25, and 50 GHz, respectively, are presented. A box-like filter response is obtained by the double- and triple-ring resonators using specific coupling coefficients.

Pseudo-Linear Transmission of High-Speed TDM Signals: 40 and 160 Gb/s

Abstract: Publisher Summary The pseudo–linear transmission is a method for the transmission of high-speed time-division multiplexed (TDM) signals where fast variations of each channel waveform with cumulative dispersion allows important averaging of the intrachannel effects of fiber nonlinearity. The pseudo–linear transmission involves complex optimization of modulation format, dispersion mapping, and nonlinearity. These transmissions occupy a space somewhere between dispersion-mapped linear transmission and nonlinear soliton transmission. The pseudo-linear regime of transmission is characterized by a rapid pulse broadening, which results in a dramatic reduction of the solitonic effect on each pulse. As a result, full dispersion compensation can be used in this regime. Extensive analysis of pseudo-linear transmission and reviews of the TDM transmission experiments at 40 and 160 Gb/s have been provided in the chapter. Two new forms of nonlinear interactions between rapidly dispersing pulses namely intrachannel cross–phase modulation (IXPM) and intrachannel four–wave mixing (IFWM) are also presented. These two intrachannel effects are the most important nonlinear interactions in pseudo-linear transmission and determine the dispersion mapping even for the wavelength–division multiplexed (WDM) systems. Further, the chapter describes the semiconductor–based technologies that enable the development of stable and reliable high–speed transmitters and receivers.

DWDM Network Designs and Engineering Solutions

Abstract: A comprehensive book on DWDM network design and implementation solutionsDesign Software Included Study various optical communication principles as well as communication methodologies in an optical fiber Design and evaluate optical components in a DWDM network Learn about the effects of noise in signal propagation, especially from OSNR and BER perspectives Design optical amplifier-based links Learn how to design optical links based on power budget Design optical links based on OSNR Design a real DWDM network with impairment due to OSNR, dispersion, and gain tilt Classify and design DWDM networks based on size and performance Understand and design nodal architectures for different classification of DWDM networks Comprehend different protocols for transport of data over the DWDM layer Learn how to test and measure different parameters in DWDM networks and optical systemsThe demand for Internet bandwidth grows as new applications, new technologies, and increased reliance on the Internet continue to rise. Dense wavelength division multiplexing (DWDM) is one technology that allows networks to gain significant amounts of bandwidth to handle this growing need. DWDM Network Designs and Engineering Solutions shows you how to take advantage of the new technology to satisfy your network's bandwidth needs. It begins by providing an understanding of DWDM technology and then goes on to teach the design, implementation, and maintenance of DWDM in a network. You will gain an understanding of how to analyze designs prior to installation to measure the impact that the technology will have on your bandwidth and network efficiency. This book bridges the gap between physical layer and network layer technologies and helps create solutions that build higher capacity and more resilient networks.Companion CD-ROM The companion CD-ROM contains a complimentary 30-day demo from VPIphotonics™ for VPItransmissionMaker™, the leading design and simulation tool for photonic components, subsystems, and DWDM transmission systems. VPItransmissionMaker contains 200 standard demos, including demos from Chapter 10, that show how to simulate and characterize devices, amplifiers, and systems.

On distributed Raman amplification for ultrabroad-band long-haul WDM systems

Abstract: We present an analysis and design method for multiwavelength pumped fiber Raman amplifiers for massive wavelength division multiplexing (WDM) systems with signal bandwidths of 10 to 12 THz and a very large number of channels. We solve self-consistently the optimal design problem for backward-pumped distributed Raman amplifiers with special gain profiles that compensate for the Raman tilt and wavelength-dependent fiber loss. We study the noise performance of these optimally designed amplifiers and address the issues of multispan amplification for long-haul transmission of such broadband signals.

Narrow-linewidth idler generation in fiber four-wave mixing and parametric amplification by dithering two pumps in opposition of phase

Abstract: Wide-bandwidth and high-gain fiber optical parametric amplifiers (OPAs) have been demonstrated recently. Their application as all-optical wavelength converters has been hampered by pump-induced converted-signal spectrum broadening, due to the required pump phase modulation. In this paper, we theoretically investigate and experimentally demonstrate a technique to cancel the converted-signal broadening by using four-wave mixing (FWM) or parametric amplification with two pumps phase-modulated 180/spl deg/ out of phase. The resulting converted-signal quality is comparable to that of the output signal.

Contention resolution for optical burst switching networks using alternative routing

Abstract: Optical burst switching (OBS) is an approach to building very high capacity routing switches based on optical data paths and electronic control. Therefore, OBS is considered as a viable solution in the high-speed optical Internet backbone. In this paper, we propose an intra-class contention resolution scheme in optical burst switching networks by the enhanced alternative routing algorithm. The blocking probability of the proposed scheme is significantly reduced as compared with the general OBS while the additional delay due to the alternative path is smaller than 10% of the basic offset time.

Dimensioning of FDL Buffers for Optical Burst Switching Nodes

Abstract: Optical burst switching (OBS) is a promising candidate for a more dynamic optical layer in the context of IP over WDM. Although buffering is not mandatory for the functionality of OBS, even simple FDL buffers can improve burst loss probability. In this paper, we first discuss principal buffer architectures and reservation schemes for fiber delay line (FDL) buffers. Then, we investigate key design parameters of FDL buffers like FDL delay, buffer architecture and total number of buffer ports. Finally, we introduce and evaluate strategies for distributing a given number of buffer ports over all FDL’s of a feed-forward buffer.

Chromatic dispersion monitoring technique using sideband optical filtering and clock phase-shift detection

Abstract: We propose and demonstrate a novel technique for 40- and 10-Gb/s chromatic dispersion monitoring that uses an optical filter to select the upper and lower vestigial-sideband (VSB) signals in the transmitted optical data and determine the relative clock phase shift caused by dispersion. Without modification of transmitters, this technique provides low cost chromatic dispersion monitoring for WDM systems, <3 ps/nm dispersion resolution for 40-Gb/s data, and greatly reduced sensitivity to the influence of polarization mode dispersion.

A generalized framework for analyzing time-space switched optical networks

Abstract: The advances in photonic switching have paved the way for realizing all-optical time switched networks. The current technology of wavelength division multiplexing (WDM) offers bandwidth granularity that matches peak electronic transmission speed by dividing the fiber bandwidth into multiple wavelengths. However, the bandwidth of a single wavelength is too large for certain traffic. Time division multiplexing (TDM) allows multiple traffic streams to share the bandwidth of a wavelength efficiently. While introducing wavelength converters and time slot interchangers to improve network blocking performance, it is often of interest to know the incremental benefits offered by every additional stage of switching. As all-optical networks in the future are expected to employ heterogeneous switching architectures, it is necessary to have a generalized network model that allows the study of such networks under a unified framework. A network model, called the trunk switched network (TSN), is proposed to facilitate the modeling and analysis of such networks. An analytical model for evaluating the blocking performance of a class of TSNs is also developed. With the proposed framework, it is shown that a significant performance improvement can be obtained with a time-space switch with no wavelength conversion in multiwavelength TDM switched networks. The framework is also extended to analyze the blocking performance of multicast tree establishment in optical networks. To the best of our knowledge, this is the first work that provides an analytical model for evaluating the blocking performance for tree establishment in an optical network. The analytical model allows a comparison between the performance of various multicast tree construction algorithms and the effects of different switch architectures.