OFC 97 explores WDM for boosting fiber bandwidth

OFC `97 explores WDM for boosting fiber bandwidth

george kotelly

The latest fiber-optic research developments, technologies, deployments, applications, and products are expected to inundate this year`s Conference on Optical Fiber Communication (OFC `97) in the Dallas Convention Center from February 15 to 21.

Network demonstrations, product presentations, exhibitor setups, and technical papers are slated to spotlight wavelength-division multiplexing (WDM) as the key show technology. According to technical program co-chair Neal Bergano, AT&T Laboratories, "The potential for WDM has been known for 20 years, but it`s only been realized as commercially viable in the last few years."

Communications providers are turning to WDM technology because it can expand the capacity of their networks without their having to install new fiber, which saves costs. What`s more, network expansion opens up bandwidth for more users to get online with today`s applications and still provides reserve capacity for emerging and future applications.

Researchers are therefore addressing the technology, subsystem, product, and application issues that promise to increase WDM reliability, flexibility, and cost-effectiveness. These issues involve single-wavelength testing, laser stability, wavelength addition and subtraction, long-distance transmission, and signal amplification, among others.

In addition to WDM technology, OFC `97 offers a showcase for researchers exploring all types of fiber-based products, optoelectronics, systems, networks, and applications. The conference is projected to break all of last year`s records in attendance, exhibitors, and technical presentations in reflecting the increasing worldwide demand for communications over fiber-optic networks. In sum, more than 370 presentations are scheduled. They include five workshops, 34 short courses, two plenary sessions, 37 invited papers, 278 contributed papers, nine tutorials, and two special symposia.

The conference is sponsored by the Optical Society of America, the Institute of Electrical and Electronics Engineers/Lasers and Electro-Optics Society, and the ieee Communications Society.

The Tuesday morning (Feb. 18) plenary session is being co-chaired by Joe C. Campbell, University of Texas at Austin, and Stephen B. Alexander, Ciena Corp. During the plenary session, two keynote speeches are scheduled. In one, Bran Ferren, executive vice president, broadband applications, Walt Disney Imagineering, will explore the important forces shaping the evolution of wideband global networks in a talk titled "There`s no bits like show bits."

In the other keynote address, "Networks and services for the future," Peter Cochrane, head of advanced research, BT Laboratories in the United Kingdom, will explain how photonics can transform the telecommunications industry by effectively making bandwidth free and distance irrelevant.

During the plenary session, the tenth John Tyndall Award will be bestowed upon Ivan Kaminow, for his contributions to lightwave device technology involving high-speed modulation, integrated optics, semiconductor lasers, fiber polarization effects, and WDM components and networks. Recently retired from Lucent Technologies` Bell Laboratories after 42 years of service as a researcher and manager, Dr. Kaminow is presently working on an Internet report for the Science Policy Research Div., Congressional Research Service of the Library of Congress.

Technical program

Based on designated subcommittee reviews, the OFC `97 technical program comprises five general categories of invited and contributed papers on optical-fiber communications and related topics, including basic research, hardware development, and system and network applications: (I) fibers, cables, and fiber-based devices; (II) optoelectronic and integrated optics devices; (III) system technologies; (IV) networks, switching, and access; and (V) applications.

The Category I subcommittee, chaired by Jay R. Simpson, Lucent Technologies, finds that add/drop multiplexing technology dominates the work done in fibers, cables, and fiber-based devices. When these devices, the amplification of an individual wavelength in multiple-wavelength networks proves a challenging task. Consequently, much of the research focuses on how to quantify the effects of WDM add/drop operation on system performance.

Some key papers in this area include one from Douglas M. Barney, Hewlett-Packard Laboratories, on the gain and noise figure characterization techniques for erbium-doped fiber amplifiers (edfas) used in WDM communications systems (WA1, Wed., Feb. 19). The paper will also cover alternate WDM test sources and the impact of excess laser noise on noise-figure measurements.

Another paper on edfas for WDM systems will be presented by Matsayuki Nishimura, Sumitomo Electric Industries Ltd., Japan (WF1, Wed., Feb.19). This paper will review the various techniques of flattening the wavelength-dependent gain and maximum usable bandwidth of edfas for achieving large-capacity WDM transmission systems.

With a view toward possible WDM applications, J.gif. Sipe and L. Rammuno at the University of Toronto, Canada, will discuss the stability and pulse output of continuous-wave and modulated fiber-grating-coupled semiconductor lasers.

The Category II subcommittee, chaired by David Dolfi, Hewlett-Packard, discovers that optoelectronic and integrated optics device research has concentrated on wavelength conversion products, lasers, photodetectors, and low-cost packaging.

Responding to wavelength conversion needs, two research teams from the Technical University of Denmark and the Alcatel Telecom Research Div., Stuttgart, Germany, combined efforts in a report on the operation of a 1.3-mm-long multiquantum-well-based, integrated Michelin interferometer wavelength converter operating at a record 40-Gbit/sec bit rate (TuO1, Tues., Feb. 18). The teams claim that the converter demonstrates non-inverted converted signals and conversion to both short and long wavelengths at a -10-dB extinction ratio and greater than a 25-dB signal-to-ASE ratio for all wavelengths.

In the field of photodetectors, Weishu Wu and colleagues at the University of California at Santa Barbara will describe the use of wafer fusion to obtain a high-gain-bandwidth-product Si/InGaAs avalanche photodetector (TuI1, Tues., Feb. 18). The device produces an 81-GHz gain-band- width-product in the 1300- to 1600-nm region.

Yet another paper will describe the work of a team of engineers at Hitachi Ltd., Tokyo, on a transfer-mold packaging technique for producing low-cost, high-performance plastic optical transmitter modules (WB3, Wed., Feb. 19). The modules consist of a silicone-gel-encapsulated subassembly that contains a silicon V-groove, an index-aligned laser diode, and a waveguide photodetector. Intermediate tests show less than a 1-dB change of 0.2-mW fiber output under severe environmental conditions.

The Category III subcommittee, chaired by John Cartledge, Queens University, Canada, summarizes that investigators are efficiently tapping into the massive bandwidth of fiber-optic networks. Refined terabit, dispersion-compensated soliton, and microwave transmissions highlight the field of system technologies.

Researchers at NEC Corp., Japan, will supply the results of a feasibility study on using both polarization modes of optical fibers for 1-bit/sec/Hz high-spectral- efficiency WDM systems (TuJ1, Tues., Feb. 18). By using optical duobinary modulation, the group has stably multiplexed 64-channel, 20-Gbit/sec signals with 20-GHz channel spacing after a 100-km transmission.

Photonic investigators at Aston University, United Kingdom, will furnish the experimental results of 10-Gbit/sec soliton propagation through 5250 km of standard and dispersion-compensating fiber to decrease the average dispersion to 0.2 psec/nm-km per amplifier span (ThN1, Thurs., Feb. 20). The single-span recirculating loop consists of 31.6 km of standard fiber, with a dispersion of +16.75 psec/nm-km at the operating wavelength of 1557 nm, and a 6.8-km dispersion-compensating module with a dispersion of -521.6 psec/nm-km.

In another 10-Gbit/sec soliton transmission study, investigators from the University of Maryland and the Laboratory for Physical Sciences, College Park, MD, will discuss a dispersion-managed, error-free, enhanced-power soliton delivery over distances to 10 million meters through mostly normal dispersion fiber in which a path-anomalous dispersion is obtained (ThN2, Thurs, Feb. 20). The transmission system encompasses a recirculating loop of four amplifier spans and five erbium-doped fiber amplifiers. Three spans contain 25 km of dispersion-shifted fiber with a normal dispersion of -1.1 psec/nm-km at 1552 nm. The fourth span has 25 km of the same dispersion-shifted fiber followed by 7 km with an anomalous dispersion of +16.5 psec/nm-km.

The Category IV subcommittee, chaired by Ray McFarland, National Security Agency, cites that the field of networks, switching, and access is maturing--last year`s studies are evolving into this year`s devices. Key network topics include WDM, the Internet, fiber-to-the-home, and future full-service.

Several engineers at NEC Corp., Japan, will report on the development of an edfa repeater for WDM networks that has a monitor for arbitrary wavelength and an acousto-optic tunable ((100 nm) filter with a high extinction ratio ((15 dB) (TuE1, Tues., Feb. 18). The repeater maintains the per-wavelength power relatively constant (+5 dBm) when the number of channels changes due to network reconfigurations or faults, which would otherwise impose a power transition in the edfa output. Receiver sensitivity degradation totals less than 3 dB for a 10-Gbit/sec transmission in the surviving channels.

Tetsuya Kanada and Shunsuke Tsutsumi at NTT Optical Network Systems Laboratories, Japan, claim in their paper that high-speed Internet will be the service driver for pushing fiber-to-the-home networks (WI4, Wed., Feb. 19). In this approach, they assert that a 100-Mbit/sec Fast Ethernet interface can be supported by an available 155-Mbit/sec, passive-optical-network (PON) access system. They also predict that future capacity demands can be satisfied with a future 1-Gbit/sec PON access system.

Applications

A new topic area for OFC `97, Applications, debuts via the efforts of the Category V subcommittee, chaired by Joseph Berthold, Bellcore. This paper-review subcommittee uncovers cost-cutting as the prime mover of the commercial development of fiber systems for long-haul, premises, and upgraded networks.

M. Oscar van Deventer and associates at KPN Research, The Netherlands, will reveal the results of four scenarios--SDM, TDM, WDM point-to-point, and WDM virtual wavelength path routing--for upgrading 2.5-Gbit/sec networks (TuL4, Tues., Feb. 18). They conclude that

the introduction of 10-Gbit/sec TDM or 4 ¥ 2.5-Gbit/sec WDM is justified by the reduction in equipment and fiber-cable km needed;

a point-to-point, 4 ¥ 2.5-Gbit/sec upgrade requires less equipment than a 10-Gbit/sec upgrade, unless low-dispersion fiber or dispersion compensation is used;

the introduction of wavelength routing is not justified, considering the moderate reduction in fiber-cable km or equipment needed compared to 4 ¥ 2.5-Gbit/sec WDM point-to-point networks.

Glenn Wellbrook, MCI Corp., will report on the continuing transmission equipment field trials for OC-192 terminals, regenerators, receiver preamplifiers, bidirectional line amplifiers, and Bragg fiber gratings in a 4-wavelength, 443-km network that implements nondispersion and dispersion-shifted fiber-optic cables (TuL6, Tues., Feb. 18). The field trials are monitoring optical amplifier system gain, signal-to-noise ratio, dispersion tolerance, bit-error rates, and system stability to determine optimal network performance.

Reportedly the longest repeaterless 2.5-Gbit/sec, submarine, fiber-optic-cable link installed for commercial service, the nearly 860-km long Cayman Island- Jamaica fiber system is slated for analysis by E. Brandon and colleagues at Alcatel Submarine Networks, Nozay, France (TuL1, Tues., Feb. 18). Comprising two point-to-point links and a branched festoon configuration (see figure on page 1), the system architecture employs forward error correction, remotely pumped amplification, and singlemode pure silica core fiber technologies. q

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