Showing papers on "Wavelength-division multiplexing published in 1998"

Fiber optic test and measurement

Abstract: This is the most authoritative, complete source of test and measurement information for engineers who design and maintain fiber optic networks.This book presents measurement principles for characterizing all three basic components of a fiber optic communication system: the optical transmitter, fiber medium and optical receiver. It also covers system level measurements, and discusses the principles and limitations of current fiber optic testing equipment. It discusses testing to SONET/SDH international standards, and helps engineers choose the best approach to testing today's new erbium doped fiber amplifiers. The book provides detailed recommendations for understanding polarization states, and presents new methods for accurately characterizing the behavior of Wavelength Division Multiplexing (WDM) fiber systems. It includes detailed coverage of testing fiber in the local loop, using optical power meters and optical time domain reflectometers. It also reviews the latest state-of-the-art 10 Gb/s systems, and even faster systems on the horizon. The coverage is practical, helping professionals accurately measure and test fiber optic systems without becoming experts in theory.

Ultra-compact Si-SiO 2 microring resonator optical channel dropping filters

Abstract: Compact optical channel dropping filters incorporating side-coupled ring resonators as small as 3 /spl mu/m in radius are realized in silicon technology. Quality factors up to 250, and a free-spectral range (FSR) as large as 24 nm are measured. Such structures can be used as fundamental building blocks in more sophisticated optical signal processing devices.

Buffering in optical packet switches

Abstract: This paper consists of a categorization of optical buffering strategies for optical packet switches, and a comparison of the performance of these strategies both with respect to packet loss/delay and bit error rate (BER) performance. Issues surrounding optical buffer implementation are discussed, and representative architectures are introduced under different categories. Conclusions are drawn about packet loss and BER performance, and about the characteristics an architecture should have to be practical. It is shown that there is a strong case for the use of optical regeneration for successful cascading of these architectures.

Understanding Optical Communications

Abstract: If you need to understand the state-of-the-art in optical communications, this is the most complete, up-to-date technical overview available. Over the past 15 years, optical fiber has revolutionized wide area communications -- making possible the Internet as we know it. Now a second fiber revolution is underway. Advanced technologies such as Wave Division Multiplexing (WDM) are adding even more capacity, and fiber is increasingly the media of choice in MANs, campuses, buildings, LANs -- soon, even homes. Now, discover the fundamental principles and components of optical communications, as well as the key interfaces and engineering challenges. Understand the roles of FDDI, Ethernet on Fiber, ESCON, Fibre Channel, SONET/SDH and ATM. Review key technical issues facing engineers as they extend fiber into new applications and markets -- and get an up-to-the-minute status report on WDM for LANs and MANs. Finally, preview the advanced R&D most likely to bear fruit: dark and spatial solitons, advanced fibers, plastic technologies, optical CDMA, TDM and packet networks, and more. Whether you're building optical systems or planning for them, this is the briefing you've been looking for.

Sinc-sampled fiber Bragg gratings for identical multiple wavelength operation

Abstract: Through a periodic sine modulation of the refractive index-profile in fiber Bragg gratings (FBGs), we demonstrate gratings with multiple equally spaced and identical wavelength channels. We show 10-cm-long gratings with 4, 8, and 16 identical uniform wavelength channels separated by the ITU spacing of 100 GHz and a 22.5-cm-long grating with four identical dispersion compensating channels with a 200-GHz separation designed to dispersion compensate 80-km data transmission through standard fiber at 1.55 /spl mu/m.

Switchable optical components

Abstract: This invention relates to a number of components, devices and networks involving integrated optics and/or half coupler technology, all of which involve the use of electronically switchable Bragg grating devices and device geometries realized using holographic polymer/dispersed liquid crystal materials. Most of the components and devices are particularly adapted for use in wavelength division multiplexing (WDM) systems and in particular for use in switchable add/drop filtering (SADF) and wavelength selective crossconnect. Attenuators, outcouplers and a variety of other devices are also provided.

Gain characteristics of tellurite-based erbium-doped fiber amplifiers for 1.5-µm broadband amplification

Abstract: The signal-gain characteristics of tellurite-based erbium-doped fiber amplifiers are clarified based on spectroscopic properties and signal-gain measurements. The potential of tellurite-based erbium-doped fiber for use as a broadband light source is also described.

Tunable optical filters for dense WDM networks

Abstract: WDM is currently taking over as the leading technology in point-to-point transmission links. For optical implementation of WDM networks, logical functionalities such as wavelength (channel) selection should be carried out in the wavelength domain; thus, the development of dynamic optical devices is required. One key device is a tunable optical filter. Important features of such a filter include low insertion loss, narrow bandwidth, high sidelobe suppression, large dynamic range, fast tuning speed, a simple control mechanism, small size, and cost effectiveness. Here, an extensive overview of the different technologies used to produce tunable optical filters is presented. Among them, fiber filters such as fiber Bragg gratings and fiber Fabry Perot are the most commercialized, yet inherently limited in their dynamic speeds. For high demanding dynamics, micro-machined and acousto-optic filters can offer a good solution for microsecond tuning speeds. Faster tunable devices, in nanosecond tuning speeds, might emerge out of microresonators, electrooptic filters, and active DBR filters.

Silica-based planar lightwave circuits

Abstract: Silica-based planar lightwave circuits (PLC) provide various important devices for both optical wavelength-division-multiplexing networks and optical access network. This paper is an overview of recent progress in PLC technology including optical power splitters, arrayed-waveguide gratings, thermooptic switches, and hybrid integrated PLC's.

Multiwavelength optical networks with limited wavelength conversion

Abstract: This paper proposes optical wavelength division multiplexed (WDM) networks with limited wavelength conversion that can efficiently support lightpaths (connections) between nodes. Each lightpath follows a route in a network and must be assigned a channel on each link along the route. The load /spl lambda//sub max/ of a set of lightpaths is the maximum over all links of the number of lightpaths that use the link. At least /spl lambda//sub max/ wavelengths will be needed to assign channels to the lightpaths. If the network has full wavelength conversion capabilities, then /spl lambda//sub max/ wavelengths are sufficient to perform the channel assignment. Ring networks with fixed wavelength conversion capability within the nodes are proposed that can support all lightpath sets with load /spl lambda//sub max/ at most W-1, where W is the number of wavelengths in each link. Ring networks with a small additional amount of wavelength conversion capability within the nodes are also proposed that allow the support of any set of lightpaths with load /spl lambda//sub max/ at most W. A star network is also proposed with fixed wavelength conversion capability at its hub node that can support all lightpath sets with load /spl lambda//sub max/ at most W. These results are extended to tree networks and networks with arbitrary topologies. This provides evidence that significant improvements in traffic-carrying capacity can be obtained in WDM networks by providing very limited wavelength conversion capability within the network.

Nonlinear Optical Communication Networks

Abstract: Optical Fiber Propagation Optical Amplifiers Optical Transmission Systems Soliton Optical Communications Repeaterless Systems Long Distance TDM Transmission WDM Optically Amplified Systems Transmission in All-Optical Networks Appendices Index

Dispersive properties of optical filters for WDM systems

Abstract: Wavelength division multiplexing (WDM) communication systems invariably require good optical filters meeting stringent requirements on their amplitude response, the ideal being a perfectly rectangular filter. To achieve high bandwidth utilization, the phase response of these filters is of equal importance, with the ideal filter having perfectly linear phase and therefore constant time delay and no dispersion. This aspect of optical filters for WDM systems has not received much attention until very recently. It is the objective of this paper to consider the phase response and resulting dispersion of optical filters in general and their impact on WDM system performance. To this end we use general concepts from linear systems, in particular, minimum and nonminimum phase response and the applicability of Hilbert transforms (also known as Kramers-Kronig relations). We analyze three different classes of optical filters, which are currently being used in WDM systems and compare their performance in terms of their phase response. Finally, we consider possible ways of linearizing the phase response without affecting the amplitude response, in an attempt to approximate the ideal filter and achieve the highest bandwidth utilization.

Gain-flattened tellurite-based EDFA with a flat amplification bandwidth of 76 nm

Abstract: It is important to flatten the gain spectrum and broaden the amplification bandwidth of Er3+-doped fiber amplifiers (EDFAs) in order to increase the transmission capacity of wavelength division multiplexing (WDM) transmission networks.

Characteristics of optical duobinary signals in terabit/s capacity, high-spectral efficiency WDM systems

Abstract: Optical duobinary signals have been applied to dense wavelength division multiplexing (WDM) systems with high-spectral efficiency to fully utilize a limited gain bandwidth of about 35 nm (4.4 THz) for an erbium-doped fiber amplifier (EDFA). These signals are one type of partial response signals and have narrower bandwidth than conventional intensity modulation (IM) signals. Thus, the use of these signals should make possible to attain ultradense WDM systems. In this paper, characteristics of optical duobinary and IM signals in ultradense WDM systems are compared through experimental evaluations at 20 Gb/s. High-spectral efficiency of 0.6 b/s/Hz was reached in this demonstration.

Multicasting optical cross connects employing splitter-and-delivery switch

Abstract: A new splitter-and-delivery (SAD) switch having multicasting capability is proposed. It is best implemented in a single silicon board using planar silica waveguide technology. Less than -40-dB crosstalk is achievable by an auxiliary action of the optical gate. Three optical cross-connect architectures employing the SAD switch are proposed. They are strictly nonblocking and have multicasting capability. Furthermore, they have wavelength or fiber modular structures and are expandable when the number of the fibers and the wavelengths increase a few or by a few times. The expanding method and other important issues are discussed in detail.

Wavelength-division multiplexing isolation fiber filter and light source using cascaded long-period fiber gratings.

Abstract: The author has successfully demonstrated a novel all-fiber wavelength-division multiplexing (WDM) isolation filter with more than 20 equally spaced loss peaks within a 60-nm band and a WDM light source with an output of 21 equally spaced wavelengths within 30% amplitude variation

Gain-flattened tellurite-based EDFA with a flat amplification bandwidth of 76 nm

Abstract: We describe a tellurite-based Er/sup 3+/-doped fiber amplifier (EDFA) with a flat amplification bandwidth of 76 nm and a noise figure of less than 7 dB. Furthermore, a parallel-type amplifier composed of this EDFA and a 1.45-/spl mu/m-band Tm/sup 3+/-doped fluoride fiber amplifier achieved a flat amplification bandwidth of 113 nm.

Dynamic spectral power equalization using micro-opto-mechanics

Abstract: We present a voltage-controlled spectral attenuator for gain shaping and power equalization in wavelength division multiplexed single-mode fiber systems. A micro-opto-mechanical modulator array, where electrostatic deflection of a silicon nitride quarter-wave dielectric layer suspended over a silicon substrate creates a column of variable reflectivity mirrors, is packaged using bulk optics and a diffraction grating to disperse the input spectrum across the device and collect the reflected light into a separate output fiber. The packaged component has 9-dB excess loss, 20-dB dynamic range and 10-/spl mu/s response. We demonstrate equalization of the amplified spontaneous emission spectrum from an erbium-doped fiber amplifier and of individual laser signals with 10-dB initial variation to less than 0.5-dB variation over a 24-nm passband-free spectrum.

Design protection for WDM optical networks

Abstract: With wavelength division multiplexing (WDM) networks the failure of a single link or component may cause the simultaneous failure of several optical channels, potentially making impossible restoration by rerouting directly in higher layers directly using the optical network (SDH, ATM, internal protocol (IP)). To address this, we introduce the concept of design protection, which aims at making such failure propagations impossible. We present the disjoint alternate path (DAP) algorithm which places optical channels in order to maximize design protection. We show the result on various network examples.

Fiber Bragg Gratingを用いた水中音波の検出

Abstract: A fiber Bragg grating (FBG), which is formed in a fiber core by introducing a periodic variation of the refractive index reflects selectively a particular wavelength of light due to the Bragg reflection. The reflected optical power is modulated if sound pressure is applied to the FBG. Using the FBG which has such a feature we made the fundamental experiments on the detection of underwater sound. Good linearity is obtained under various conditions with the insertion of optical isolators that avoid the fluctuation of detected output due to the Fabry-Perot interference effect between the FBG and the various facets. The sensitivity of detection is maximized if the slope of the curve in the transmittance-wavelength characteristics is steepest at the operating wavelength. Simultaneous multiplex detection is made possible by wavelength division multiplexing with two FBGs in series connection.

Method and apparatus for determining the shape of a flexible body

Abstract: A fiber optic measurement system capable of greatly improving the cost, complexity, and efficiency with which flexible body shape estimates are made. The fiber optic shape measurement system uses Bragg grating sensor technology and time, spatial, and wavelength division multiplexing, to produce a plurality of strain measurements along one fiber path. Using a plurality of fibers, shape determination of the body and the tow cable can be made with minimal ambiguity. Also disclosed is a method to resolve the body shape based on strain-to-shape structural analysis. Possible applications include, but are not limited to, sensing the shape and position of flexible bodies, aid in improving the efficiency of existing acoustic surveying processing techniques, and related applications in geophysical prospecting.

Optimal design and evaluation of survivable WDM transport networks

Abstract: This paper proposes an optimal design scheme for survivable wavelength-division multiplexing (WDM) transport networks in which fast restoration can be achieved by using predetermined restoration paths that are independent of failure locations and which have one to one correspondence with working paths Integer programming-based design problems are formulated to optimally determine working and their corresponding restoration paths, the number of fibers in each span, and the number of optical cross connects (OXCs) in each node In these optimization problems, total facility cost, which includes not only transmission cost but also cross connection, is minimized This design scheme can handle the dedicated/shared allocation of spare resources and several parameters, such as the maximum available number of wavelengths per fiber /spl Omega/, the matrix size of each OXC, and cross-connection to transmission cost-coefficient ratio /spl gamma/ Total fiber length, the total number of OXCs, etc, are evaluated from obtained design results for these options and parameters Numerical examples show that the dependency of total fiber length and the total number of OXCs on /spl gamma/ is relatively small, and cross-connection to transmission cost ratios (/spl gamma/ times the total number of OXCs divided by total fiber length) in the dedicated and shared cases are almost the same for each combination of /spl gamma/ and /spl Omega/

Wavelength-division-multiplexed passive optical network based on spectrum-slicing techniques

Abstract: We propose and demonstrate a new wavelength division-multiplexed (WDM) passive optical network (PON) architecture that uses N/spl times/N waveguide grating routers (WGRs) in the remote node and central office for simultaneous multiplexing and demultiplexing of N-1 channels in each direction. In the demonstrated network, a spectrum-sliced fiber amplifier light source was used to transmit 15 downstream channels operating at 500 Mb/s. The 155-Mb/s upstream channels used 1.5-/spl mu/m LED's. In addition, an erbium-doped fiber amplifier was used at the, central office to compensate the slicing losses of low-power LED's. The crosstalk, caused by using WGR's for both multiplexing and demultiplexing channels, was suppressed to a negligible level by using two types of bandpass filters. There was no significant degradation in the receiver sensitivity caused by this crosstalk.

Silicon oxynitride planar waveguiding structures for application in optical communication

Abstract: The refractive index of silicon oxynitride (SiON), a widely used material for integrated optics devices, can be chosen in a wide range between 1.45-2.0. We describe how the consequent large design freedom can be exploited on the one hand for a "standard" polarization independent optical channel waveguide having a favorable tradeoff between efficient fiberchip coupling and small bend radii (compact devices) and on the other hand for special-purpose and hybrid components where the refractive index should be finely adjusted for obtaining the desired functionality. We illustrate the applicability of SiON by describing a few devices for optical filtering in a new architecture for wavelength multiplexing, modulation, polarization splitting and second-harmonic generation.

A millimeter-wave full-duplex fiber-radio star-tree architecture incorporating WDM and SCM

Abstract: We propose a full-duplex millimeter-wave fiber-radio network for providing wireless customer access to broadband services. It consists of a hybrid star-tree architecture connecting remote antenna base stations to a central control office (CO) by incorporating wavelength-division multiplexing (WDM) of the optical signals and subcarrier multiplexing (SCM) of the radio signals. These multiplexing schemes allow the sharing of equipment at the CO and therefore enable a simple radio distribution architecture to be implemented. We also demonstrate a 35.5-39.5-GHz full-duplex fiber-radio star-tree network, featuring three WDM carriers in the downstream and a single carrier in the upstream. Each downstream wavelength carries three 155-Mb/s BPSK SCM channels between 35.8-39.3 GHz, while a 37-GHz carrier transports 51.8 Mb/s upstream.

Wavelength assignment for dynamic traffic in multi-fiber WDM networks

Abstract: We propose an on-line wavelength assignment algorithm for multi-fiber WDM networks, in which lightpaths are established and released dynamically. For a given number of fibers per link and number of wavelengths per fiber, the algorithm aims to minimize the blocking probability. It may also be used to reduce the number of wavelengths required for a given tolerable blocking probability. Simulation results show that our wavelength assignment algorithm performs better than other previously proposed algorithms (in the cases we studied). As the number of fibers per link increases, the benefit of having wavelength converters decreases dramatically, and the performance improvement of our algorithm over others increases. Our results also show that in case a preferred path is not available, rerouting along a node-disjoint backup path can significantly reduce the blocking probability.

A widely tunable narrow linewidth semiconductor fiber ring laser

Abstract: We have demonstrated a novel approach to obtain a 0.1-nm line width laser with 38-dB sidemode suppression by utilizing a 1.3-/spl mu/m semiconductor optical amplifier in a fiber unidirectional ring that consists of a linear polarizer and polarization controllers. The laser has a low-threshold current of 22.5 mA as well as a wide tuning range of 28 nm. The new approach is applicable to the 1.55-/spl mu/m region as well. It is expected that nanosecond wavelength tuning speed is feasible using this approach in conjunction with fast electrooptic polarization controllers, short cavities and low-cavity losses.

Highly selective and widely tunable 1.55-μm InP/air-gap micromachined Fabry-Perot filter for optical communications

Abstract: The authors report, for the first time, a highly selective and widely tunable optical filter at 1.55 /spl mu/m using a Fabry-Perot resonator with micromachined InP/air-gap distributed Bragg reflectors. The minimum resonance full-width at half-maximum (FWHM), as measured by microreflectivity experiments, is close to 0.4 mm (around 1.55 /spl mu/m) and is compatible with wavelength-division multiplexing specifications of optical telecommunications. The tuning range is 62 nm for a tuning voltage of 14 V. The FWHM is kept below 1 nm over a 40 nm tuning range.

Optical amplifier having first and second stages and an attenuator controlled based on the gains of the first and second stages

Abstract: An optical amplifier is disclosed having substantially uniform spectral gain. The amplifier comprises a variable optical attenuator coupled between first and second segments of active optical fiber. The attenuation of the optical attenuator is adjusted in accordance with the optical power input to the amplifier to thereby obtain substantially flattened gain. Alternatively, the attenuator can be controlled based on the respective gains associated with the first and second segments of optical fiber. For example, the attenuator can be adjusted so that so that the sum of the two gains remains substantially constant, a condition that also yields flat spectral gain. Further, optical powers associated with first and second wavelengths of amplified stimulated emission (ASE) light output from the amplifier can be used to adjust the attenuation of the optical attenuator. In an additional example, received optical powers associated with each of the channels in a WDM system arc monitored and the attenuators within each amplifier in the system are controlled so that the received powers are substantially equal.

Code division multiplexing lightwave networks based upon optical code conversion

Abstract: Lightwave networks realized through code division multiple access techniques are extensively studied to determine their ultimate capabilities. Here, these concepts are extended to network implementation by introducing an optical code division multiplexing (OCDM) multihop strategy using optical coding. It is shown that this approach is effective in scaling up existing wavelength division multiplexing (WDM) networks without a significant drain of the wavelength resources. The concept of a virtual optical code path (VOCP) is introduced within the transport layer of the network. It is demonstrated that this is a potential solution to wavelength path (WP) allocation problems which may plague WDM based transport networks of the future. Crucial to the VOCP concept is optical code conversion. The interplay between this added functionality and the optical cross-connect is highlighted; the optical cross-connect serves to establish VOCP/VWP (virtual wavelength path) in the hybrid transport layer. An example of optical code conversion is introduced. It is based on coherent OCDM principles in which bipolar phase-shift keyed (PSK) optical pulse sequences are used as the signature codes. Error-free code conversion using a four-chip optical encoder/decoder is successfully performed at 1.24 Gbit/s. The results show the feasibility of high bit rate OCDM transmission with optical code conversion.