OFC 96 assesses latest fiber-optic technology, components and networks

OFC `96 assesses latest fiber-optic technology, components and networks

GEORGE KOTELLY

Leading-edge fiber-optic technology, products and networks are expected to receive their annual appraisal by an estimated 6000 attendees at the 1996 Optical Fiber Communications (OFC `96) conference. Live network demonstrations, product presentations, more than 200 exhibitor displays and more than 260 technical papers are going to highlight how fiber-optic network research, systems applications and product commercialization issues will deliver future communications services.

"It`s essential that people know the options to design cheaper and more-effective systems," says Kenneth Hill of Communications Research Center in Canada and OFC `96 technical program cochair. Andrew Chraplyvy of AT&T Bell Laboratories is the other cochair.

OFC `96 will be held in the San Jose Convention Center in San Jose, CA, from February 25 to March 1. It is sponsored by the Optical Society of America, the Institute of Electrical and Electronics Engineers Communications Society and the IEEE/Lasers and Electro-Optics Society.

Presented on Sunday, February 25, from 1 to 5 p.m., four preconference workshops will cover broadband local access networks, modeling of lightwave systems, optical networks and wavelength-division multiplexing, or WDM, technology issues. On Friday, March 1, the second international workshop on optical networking will be held from 10:30 a.m. to 6 p.m.

Starting on Monday, February 26, with a full day`s itinerary, and continuing with a lighter schedule on Tuesday, February 27, and Wednesday, February 28, approximately 32 three-hour short courses will be presented by leading fiber-optic company managers and engineers. The course subjects will encompass virtually all of the important optical industry trends and issues, ranging from introductory to expert knowledge, and should be of special interest to technical, cable-TV and regional Bell operating company personnel.

During the plenary session on Tuesday morning, the ninth John Tyndall Award will be presented to Kenneth Hill, principal scientist at the Communications Research Center, Ottawa, Canada, for the discovery of photosensitivity in optical fibers and its application to Bragg gratings used in device applications for optical communications and sensor systems.

The OFC plenary speaker is James L. Barksdale, president and chief executive at Netscape Communications Corp. in Mountain View, CA. He will talk about what is driving the need for more bandwidth on the World Wide Web.

In the exhibit hall, more than 200 companies are expected to fill exhibit booths with new and leading-edge fiber-based products and services. Exhibit hours start on Tuesday and continue through Thursday.

Now in its third year, the popular OFC Commercial Technology Program is offering 14 sessions that aim at the end user of fiber-optic technology. The four Tuesday sessions cover field splicing and testing, a fiber-optic primer, fiber optics in the subscriber loop and the economics of fiber optics. The six Wednesday sessions involve network fundamentals, access architecture alternatives, management of all-optical networks, fiber and wireless cost factors of fiber-optic communications networks and parallel data processing. On Thursday, four sessions deal with fiber to the desk, optical fiber sensor technology and applications, bandwidth and parallel data processing.

A conference staple, the OFC tutorials cover emerging fiber and optical technologies and are taught by world-renowned experts. Eleven one-hour tutorials are being held Tuesday to Friday and encompass network fundamentals, undersea lightwave systems, wavelength-conversion techniques, broadband architectures and technologies, time-domain reflectometry, dispersion compensation in nonlinear systems, optical network architectures, semiconductor components for WDM systems, high-power fiber amplifiers and lasers, integrated silica waveguide technologies and fiber devices.

In the OFC `96 technical program, more than 260 presentations are scheduled in four general categories: fiber, cables and fiber components; optoelectronic and integrated optics devices and components; system technologies; and networks and switching.

Live demonstration

Among the exhibitions will be a live network demonstration running in the exhibit hall. It will feature a reconfigurable, four-wavelength, 10-gigabit-per-second, optically switched network test bed built by the research, science and university laboratory members of the Optical Network Technology Consortium and the National Transparent Optical Network Consortium.

The network consists of a wavelength-routed, transparent, all-optical inner core architecture through which signals pass independent of their modulation format or data protocol. Transmission through the inner core is controlled by the states of several WDM crossconnect switches that allow optical connectivity independent of the fiber connections.

Logical network operations, such as circuit or asynchronous transfer mode, or ATM, cell switching, are performed in four synchronous optical network/ATM access nodes interconnected by two fiber rings using four wavelength transmission and transparent optical switches. Optical connectivity is controlled by a graphical user interface network management console.

Poster papers

A poster session will be held from 4 to 5:30 p.m. on Wednesday in the exhibit hall. In this session, authors are each provided with a 4- by 8-foot bulletin board on which to summarize their papers` research and results. Authors remain next to the bulletin boards to answer attendees` comments. Three concurrent oral poster preview sessions will take place from 3:30 to 4 p.m. prior to the poster session.

Although tendered too late for inclusion in the OFC `96 technical program, a limited number of postdeadline papers, which detail new and important material in rapidly advancing optical areas, will be presented Thursday, at 5:30 to 7 p.m.

Technical paper roundup

Here`s a brief summary of technical papers judged as of special interest to Lightwave readers.

For the Tuesday session on Transmission Systems, engineers at BNR Europe Ltd. in the United Kingdom have modeled and experimentally compared a 40-Gbit/sec optical time-domain multiplexing system over a transmission distance of 560 kilometers. They predicted a signal wavelength tolerance window of 3 nanometers with positive modulator chirp for 3 to 6 decibel relative to milliwatt optical power, 4- to 6-dB amplifier noise figure and 0.3 picosecond/km1/2 fiber polarization-mode dispersion. System Q-factors in excess of 6.3x10-16 bit-error rate were achieved using dispersion-shifted fiber over a wavelength range of 3 nm.

Japanese researchers at Mitsubishi Electric Corp. have carried out 10-Gbit/sec repeaterless transmissions over 258 km using 24-psec return-to-zero pulses. They experimentally achieved a high receiver sensitivity of 103 photons/bit at a 60.8-dB loss budget.

Other researchers at AT&T Bell Laboratories have developed a 1.3-micron Raman amplifier with improved system performance. They describe a bit-error test made on the amplifier with gains of 29 dB and output powers exceeding +15 dBm.

In another session paper, Japanese researchers at NTT Optical Network System Laboratories have equalized 4.4-psec through a 20-Gbit/sec line with 100-km line-amplifier spacing. The equalized pulse width after transmission was 6.9 psec.

Another team of researchers at AT&T Bell Laboratories will report on the design and development of a circulator-based, bidirectional optical amplifier. They used the amplifier as a midspan repeater to demonstrate a bit-error-rate transmission of 10-13 at 10 Gbits/sec over 240 km of dispersion-shifted fiber in both directions at channel wavelengths of 1557.5 and 1559 nm.

Other NTT Optical Network Systems Laboratories` engineers have demonstrated the transmission of 10 channels of 10-Gbit/sec signals over a 1200-km link of dispersion-shifted fiber with 100-km repeater spacing. By employing spectrally flat gain erbium-doped fiber amplifiers with a high aluminum concentration as repeaters, they eliminated signal gain equalization and pre-emphasis.

For the Tuesday session on Network Architecture and Performance, a group of investigators from MIT Lincoln Laboratories will present the performance results of a 2.5-Gbit/sec, circuit-switched wavelength-division multiplexed, 20-channel, all-optical test bed. They obtained more than a 19.9-Gbit/sec aggregate data rate and uniform performance over local area broadcast and metropolitan area routed and broadcast modes.

Progress in fiber amplifiers is covered in a Tuesday afternoon session. Work done by C. Hodgson at Stanford University and A. Vengsarkar at AT&T Bell Laboratories shows that amplified spontaneous emission sources with intermediate long-period fiber gratings in doped fibers provide powers exceeding 20 milliwatts, a broad spectrum of more than 35 nm, a short coherent length of less than 15 microns and a spectral shape that can be tailored to the application.

A team of engineers from AT&T Bell Laboratories, SDL Inc. and Polaroid Corp. have focused efforts on the development of ultrahigh-power, diode-pumped 1.5-micron fiber amplifiers. The team`s measurements reveal that the fiber amplifiers yielded powers to 4 watts (+36 dBm for a 2.5-Gbit/sec transmission experiment with a two-stage amplifier possessing a output power of 2.5 watts).

Investigators at SDL Inc. will describe a 650-milliwatt, fiber-coupled, master oscillator power amplifier laser diode that was used to pump an erbium-doped fiber amplifier. They obtained output powers to +24.8 dBm at a 1.55-micron wavelength.

The Tuesday afternoon session on WDM systems will start with a paper from Hitachi Ltd. Japanese researchers have studied the impact of cross-phase modulation on WDM transmission over dispersion-shifted fiber. They claim that the 10-Gbit/sec four-channel WDM transmission experiment showed serious transmission degradation when cross-phase modulation was combined with typical variation of dispersion-shifted fiber.

Another Japanese team from NEC Corp. will describe the measurement of bit-error-rate impairment resulting from dynamic cross-phase modulation under high-power, 2.5-Gbit/sec, WDM signal transmission in conventional fiber. They have assessed the dependence of the power penalty on transmitted power, channel spacing and number of channels.

Northwestern University engineers will present their analysis of channel crosstalk in wavelength-multiplexed subcarrier systems for channel spacings of 2 to 16 nm. A new crosstalk mechanism--the Kerr-shutter effect due to cross-phase modulation and mode coupling between modes--is proposed to explain the large crosstalk at small channel spacings.

In an invited paper, A. Gnauck of AT&T Bell Laboratories will outline the technical challenges facing amplified lightwave systems that incorporate WDM techniques to increase system capacity. He will also review experiments that have pushed the throughput of amplified optical fiber links to one-third of a terabit/sec.

Investigators from Japan`s NTT Optical Network Systems Laboratories have verified the suppression of four-wave mixing through a submarine cable with dispersion-managed fiber-optic cable through 50-Gbit/sec WDM transmission over 905 km and 20-Gbit/sec WDM transmission over 2715 km.

Advances in optical fibers and cables are covered in a late afternoon Tuesday session. By optimizing deposition temperature, sintering temperature and torch velocity in a high-processing-rate, two-step modified chemical vapor deposition, AT&T Bell Laboratories` engineers have attained the lowest reported index depression of 0.71%.

M. Smith at Spectran Corp. will propose a hollow, all-glass waveguide manufacturable from a drawn preform for 2.9-micron laser transmission. Using a Bragg reflector as the wall of the hollow core, he has achieved an attenuation of less than 1 dBm.

Engineers at Japan`s Kanagawa Academy of Science and Technology will report on a large-core, high-bandwidth polymer optical fiber that has an attenuation of transmission of less than 50 dB/km at a 1.3-micron wavelength.

In an invited paper for the Tuesday session on OEIC Receivers and Photodetectors, S. Chandrasekhar at AT&T Bell Laboratories will review the progress and status of monolithic photoreceivers that incorporate photodetectors with preamplifier electronics. The photoreceivers cover data rates from 100 megabits per second to 20 Gbits/sec in single-channel and multichannel configurations. He will also discuss the integration of guided wave devices with photoreceivers for WDM applications.

Investigators from the Swiss Federal Institute of Technology in Zurich have fabricated a monolithically integrated indium phosphide-based pin-HEMT OSIC receiver with a bandwidth of 18 gigahertz.

At Japan`s NTT Opto-Electronics Laboratories, engineers have built a hybrid-integrated photoreceiver with an 8-GHz bandwidth using a silica-based planar-lightwave circuit platform and a monolithic photoreceiver. They claim that the photoreceiver is the first platform of its type to operate at 10 Gbits/sec.

Another Japanese team from NEC Corp. is going to describe an 8-channel-array optical receiver for star topology access networks. The team obtained a receiver dynamic range of 21.6 dB and an allowable interchannel receiving power difference of 16.6 dB at 155 Mbits/sec. These characteristics allowed the structuring of a fiber-in-the-loop system with a serving area of 7.2 km.

Researchers from the University of Texas in Austin will cover a grating-coupled, normal incidence, horizontal-resonant cavity photodetector. The device`s characteristics include a 2-Angstrom, full-width at half-maximum bandwidth of the spectrum and a 30-Angstrom tunable range of resonance.

Long-haul transmission

The Tuesday session on long-haul transmission starts with a paper from investigators at AT&T Bell Laboratories who have improved the performance of long-haul optical amplifier transmission systems by using bit-synchronous polarization and phase modulation. Tested systems transmitted 100-Gbits/sec, made up of 20 5-Gbit/sec WDM channels, over 6300 km.

Researchers at Alcatel Submarine Networks in the United Kingdom will report on their successful operation of 5-Gbit/sec transmission over 15,200 km through an optically amplified submarine cable system.

Another AT&T Bell Laboratories team will summarize its WDM transmission tests made on portions of the Trans-Pacific Cable (TCP-5) and Trans-Atlantic Cable (TAT-12) systems. Tests were performed at transmission rates to 30 Gbits/sec over distances to 16,800 km by looping the received signal back at the ends of the undersea plant.

Japanese engineers at Fujitsu Laboratories Ltd. have demonstrated 20-Gbit/sec transmissions over 2040 km using both optical time-division modulation and conventional time-division modulation techniques.

Another AT&T Bell Laboratories team will report on field demonstrations of 10-Gbit/sec transmitters, receivers and a high-speed polarization scrambler that enabled long-term error-free transmission with a bit-error rate below 10-15 on a 4230-km long TCP-5 cable and a bit-error rate of 10-11 for 8460-km transmission.

Still another AT&T Bell Laboratories team will describe monitoring techniques for next-generation, WDM, undersea communications systems. The team will present experimental results on using a separate side-tone wavelength to monitor small degradations in a 2100-km, 4x2.5-Gbit/sec, WDM optically amplified system.

Engineers at the University of Southern California have analyzed the transmission degradations due to fiber-dispersion effects for dispersion-managed WDM systems at 5, 10 and 20 Gbits/sec. They found that cross-phase modulation is the major degrading effect in 5-Gbit/sec transmission, both cross-phase modulation and dispersion degrade system performance in 10-Gbit/sec transmission, and fiber dispersion is the key degrading effect in 20-Gbit/sec transmission.

Another AT&T Bell laboratories team will offer details on a directly modulated, distributed feedback laser operating at 2.5 Gbits/sec in a 465-km, repeaterless transmission system. The system uses remote post- and preamplifiers and dispersion-compensating fiber.

Undersea systems

Three invited papers underscore the Wednesday session on undersea transmission systems. In the first paper, P. Trischitta at AT&T Bell Laboratories will cover the new generation of undersea systems using the latest developments in fiber-optic and networking technologies. He will also explore the global undersea communications systems expected by the turn of the century.

In the session`s second paper, E. Desurvire, J.-P. Hamaide and E. Brun at Alcatel-Alsthom Recherche in France will report on soliton transmission for future undersea systems running at bit rates exceeding 100 Gbits/sec and employing amplifier/repeater spacings of more than 60 to 100 km and functioning with wavelength-division multiplexing and network routing.

S. Saito at NTT Optical Network Systems Laboratories in Japan will present the session`s third paper on comparing non-return-to-zero and soliton-transmission techniques for 1000- to 10,000-km long optical networks in terms of performance limitations, remedies and future enhancements.

Optical processing

Optical processing and interconnects are the subjects of a Wednesday session. The session leads off with a paper by Japanese researchers at NTT Optical Network Systems Laboratories who have demonstrated polarization-independent, all-optical TDM demultiplexing to 200 Gbits/sec. They achieved less than 0.5-dB polarization dependency by using four-wave mixing in depolarized TE and TM modes via a traveling-wave semiconductor laser amplifier.

Investigators at Heinrich-Hertz-Institut fur Nachrichtentechnik Berlin GmbH in Germany have demultiplexed a 40-Gbit/sec time-division-multiplexed signal to 10 Gbits/sec using a single mode-locked semiconductor laser operating as an all-optical clock recovery unit. The pulses from the mode-locked laser directly controlled a monolithically integrated all-optical demultiplexer.

University of Southern California researchers will discuss wavelength shifting over 9 nm for two microwave subcarriers by using four-wave mixing in a semiconductor optical amplifier at a power penalty of 0.5 dB. They also found that the radio-frequency spectrum was unaffected by wavelength shifting.

S. Kawanishi at NTT Transmission Systems Laboratories in Japan will report on progress made in 100-Gbit/sec optical transmission experiments. He will review ultrashort pulse generation, high-speed timing extraction and all-optical multiplexing/ demultiplexing.

Access networks

Access network design and operation are slated for a Wednesday session. In one paper, a multinational group of engineers from Telenor AS in Norway; Ericsson in Sweden; Nokia Research, KPN, and Telecom Finland; CSELT in Italy; CNET in France; and the University of Athens have consolidated efforts on technoeconomic analyses of broadband access network upgrade alternatives for public network operators and cable-TV operators. The engineers studied fiber, coaxial-cable and twisted-pair copper media for delivering the same set of services.

In an invited paper, N. Frigo at AT&T Bell Laboratories will review passive optical network proposals that address cost and operations issues for the local loop. He declares that recent component, architecture and service developments might make WDM passive optical networks a competitive delivery option.

Other researchers at AT&T Bell Laboratories will recount their development of low-cost, mini-fiber nodes deep into coaxial-cable distribution networks. They have developed a hybrid fiber/coaxial cable upgrade strategy that appears to solve upstream limitations and increases overall system bandwidth without affecting existing systems and their operations.

Investigators at AT&T Bell Laboratories and AT&T Network Cable Systems have come up with a passive optical network in which broadcast digital video is provided as a low-cost overlay to baseband digital-switched services. They have demonstrated that more than 150 Motion Picture Experts Group-2 encoded video channels can be transmitted using an inexpensive Fabry-Perot laser and subcarrier modulation. Video and switched services are detected on the same receiver in the optical network unit.

Another team at AT&T Bell Laboratories will report on an amplified star network based on remote, shared pumping of an erbium-doped fiber located within the passive distribution plant. They have found that better system sensitivity was obtained with this system than with locally pumped preamplifiers, whereas shared pumping provides satisfactory tolerance-to-pump failure.

Dispersion-compensating fibers and their applications receive attention at a Thursday session. In an invited paper, M. Nishimura and M. Onishi at Sumitomo Electric Industries Ltd. in Japan will review the performance and potential applications of dispersion-compensating fiber.

Other researchers at Sumitomo will explore optimum structures of dispersion-compensating fibers and self-phase modulation. They have confirmed that a structure with an enhanced figure of merit of 280 psec/nm/dB benefits self-phase modulation suppression.

Another study team from Furukawa Electric Co. Ltd. in Japan will report on how they used W-shaped profiles to obtain dispersion-compensating fiber of high negative dispersion (less than -160 psec/nm/km), high FOM (greater than 300 psec/nm/dB), or dispersion flat compensation from 1.53 to 1.56 microns. The team proposes that the nonlinear properties of W-shaped dispersion-compensating fibers are superior to those of matched-clad dispersion-compensating fibers.

A paper from investigators at Corning Inc. will compare the measured ratio of nonlinear refractive index and effective area in optical fibers for lightwave systems operating at 1550 nm for dispersion-shifted fibers, large effective area dispersion-shifted fibers and dispersion-compensating fibers.

United Kingdom researchers at the University of Southampton and BT Laboratories will describe how they achieved dispersion compensation at 10 Gbits/sec over 400 km of nondispersion-shifted fiber using a 10-centimeter-long, chirped, apodized, fiber Bragg grating.

In a Thursday session, WDM crossconnects receive close observation. In an invited paper, J. Berthold at Bell Communications Research will assert that applications that drive acceptance of WDM networking technology in local exchange networks are likely to be different from those in long-distance networks.

A France Telecom group is proposing an experimental test bed of wavelength routing using wavelength conversion devices. Results concerning cascading and transmission limitations at 2.5 Gbits/sec on singlemode standard fiber will be given.q