OFC 95 showcases live all-optical network demonstrations on exhibit floor

OFC `95 showcases live all-optical network demonstrations on exhibit floor

George Kotelly

Optical fiber research, development and deployment solutions precipitate the theme of the 1995 Optical Fiber Communications (OFC `95) conference. Live network demonstrations, product displays, seminars and papers are highlighting how fiber-optic network research, systems applications and commercialization issues will deliver future telecommunications services.

OFC `95 will be held February 26 to March 3 in the San Diego Convention Center. It 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.

Four pre-conference workshops will be presented on Sunday, February 26. These workshops will enable attendees to discuss leading topics with colleagues and will cover broadband local access networks; the role of fiber in wireless communications; operation, administration, maintenance and provisioning in lightwave systems using optical amplifiers; and ultra-high bit-rate systems.

Starting on Monday, February 27, with a full day`s itinerary, and tapering off on Tuesday and Wednesday, more than 30 three-hour short courses will be presented by leading fiber-optic company managers and engineers. The course subjects will encompass virtually all of the salient optical industry trends and issues, ranging from introductory to expert knowledge.

The plenary session on Tuesday will be co-chaired by Richard Lowe at Northern Telecom Canada Ltd. and N. Anders Olsson at AT&T Bell Laboratories.

During the plenary session, the John Tyndall Award will be presented to Tingye Li, head of the lightwave systems research department at AT&T, for sustained advances in high-capacity optical-fiber communications systems created by pioneering research, leadership and personal contributions during more than two decades.

In addition, Arno Penzias, vice president for research at AT&T Bell Laboratories will talk about emerging information technologies and their impact and possibilities for business and society.

From Tuesday through Thursday in Exhibit Hall C, more than 200 companies are expected to fill exhibit booths with new and leading-edge fiber-based products and services.

Brought back for the second year by popular demand, the OFC Commercial Technology Program is offering five informal sessions that tackle the business issues involving fiber-optic products and applications. The three Tuesday sessions cover telecommunications/synchronous optical network/synchronous digital hierarchy, integration and installation of a fiber network, and data communications. The two Wednesday sessions involve video, and fiber and wireless interactions.

The OFC tutorials--a conference staple"--cover emerging fiber and optical technologies and are taught by world-renowned experts. This year`s 10 one-hour tutorials are spread over Tuesday through Friday, March 3, and encompass state-of-the-art lightwave developments.

In the OFC `95 technical program, more than 275 presentations are scheduled in four categories-fiber, cables and fiber components; opto-electronic and integrated optics devices and components; system technologies; and networks and switching.

Live demonstration

An outstanding exhibition of OFC `95 will be two live network demonstrations running in the exhibit hall. One demonstration will feature a reconfigurable, multiwavelength all-optical-network test bed built by the nine research, science and university laboratory members of the Optical Network Technology Consortium and sponsored by the U.S. Advanced Research Projects Agency.

The Optical Network Technology Consortium 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 wavelength-division multiplexer crossconnect switches that allow optical connectivity independent of the fiber connections.

Logical network operations, such as circuit or asynchronous transfer mode cell switching, are performed in four Sonet/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. According to Charles Brackett, executive director, optical networking research, for Bell Communications Research, "This technology is only one, hard cycle away from commercial application."

The other live demonstration involves the Rainbow 2 1-gigabit-per-second, metro politan area all-optical network based on a broadcast-star architecture (see Lightwave, January 1995, page 1). Jointly designed and developed by IBM and the Los Alamos National Laboratory, the network consists of optical network adapters that provide connectivity to host computers using the high-performance parallel interface protocol. Each adapter transmits data at a special optical wavelength, and these transmissions are broadcast to all the adapters by a passive-star coupler. A tunable filter is used at each adapter to select the desired wavelength.

Although tendered late in the OFC `95 program, the ever-popular "Post-Deadline Papers," which detail the latest developments in rapidly advancing optical technologies, will be administered Thursday, March 2, at 4:30 to 6 p.m.

Wavelength-division multiplexing

Research on wavelength-division multiplexing continues to attract funds and studies as 2.5-Gbit/sec networks look to jump to 10 Gbits/sec using the same network infrastructure. Reflecting the widespread interest in wavelength-division multiplexers, the Tuesday session has morning and afternoon parts.

In Part 1, engineers at Bell Laboratories have carried out experimental and numerical studies that compare the behavior of erbium-doped fiber amplifiers at 980 and 1480 nanometers for wavelength-division multiplexing systems. Their results disclose that for a 15-nm bandwidth, the signal-to-noise spectrum for fixed 26.7-decibel attenuation, simulating a fiber span of 131 kilometers, is flatter for 1480-nm pumping. For the more realistic case of a 21.7-dB span loss, representing a fiber span of 106 km, the signal-to-noise ratios were higher and flatter for 980-nm pumping.

Three other researchers at Bell Laboratories looked at the potential of using wavelength-division multiplexing techniques to increase the capacity of installed optical amplifier systems. To that end, they added a second 2.5-Gbit/sec channel to one line of the Americas-1N 2100-km undersea system, which connects Vero Beach, FL, to the island of St. Thomas in the U.S. Virgin Islands, to double system capacity and length by looping the system back on itself at one end. Bit-error ratio performance was found to be better than 10-12 for both channels.

In another paper, Bellcore researchers joined forces with City University of New York. They discovered that the requirements on laser and optical filter misalignments for wavelength-division multiplexing systems with two grating-based optical filters were almost the same at 2.5 and 10 Gbits/sec per optical channel. In addition, the team shows that laser misalignments of approximately 䕂 gigahert¥ for 25-GH¥fiber misalignments produce a 1-dB system power penalty.

In Part 2, Nippon Telegraph and Telephone Optical Network Systems Laboratories` engineers will describe the successful transmission of 10 channels of 10-Gbit/sec optical frequency-division-multiplexed signals over 550 km of dispersion-shifted fiber. By employing unequal channel spacing and gain equalization without intentional dispersion management, the group observed no power penalties on any channel.

Work done by another Bellcore-City University of New York team focuses on the development of a gain-equalized, eight-wavelength optical add/drop multiplexer. The team`s measurements reveal that the gain of a 1480-nm-pumped erbium-doped fiber amplifier in the wavelength-division multiplexer-add/drop multiplexer is equalized to within 1 dB over a 20-nm optical bandwidth for total input signal power variations of 8 dB, or for pump power variations of 1 dB. Also measured were variations of 1.6 dB in the output signal powers because of polarization-dependent losses.

Investigators at Mitsubishi Electric Corp. in Japan will describe 8-channel, 2.5-Gbit/sec wavelength-division multiplexer transmission experiments over 275 km of fiber using directly modulated 1.55-micron distributed feedback laser diodes and a 0.98-micron pumped erbium-doped fiber amplifier repeater. A 1.3-micron zero-dispersion singlemode fiber placed after the transmitter section effectively suppresses four-wave mixing.

In an invited paper, J. Wiesenfeld, B. Glance, J. Perino and A. Gnauck at Bell Laboratories will review all-optical wavelength conversion techniques in high-speed wavelength-division multiplexer systems. Some of the described techniques include cross-gain and phase modulation in semiconductor optical amplifiers and lasers, as well as four-wave mixing in semiconductor devices and optical fibers.

Another Bell Laboratories` team will disclose its successful demonstration of launching high optical power (greater than 22 decibel meters) into dispersion-shifted fiber using spectrum-sliced fiber amplifier light sources, resulting in long-distance transmissions (300 km at 2.5 Gbits/sec) without the need of repeating amplifiers.

University of California Department of Electrical Engineering and Computer Sciences researchers will present their analysis of using a filter-bank receiver to cancel the interference arising in dense wavelength-division multiplexer systems from the limited stop-band rejection of optical filters. Their scheme cuts the crosstalk-induced power penalty by approximately one-half, or decreases the channel spacing by about one-third.

Emerging technology

Integrated modulators, a major research area, is covered in a Tuesday session.

Bell Laboratories` and Columbia University Department of Physics` researchers teamed up to measure the two-tone intermodulation distortion of an integrated distributed Bragg reflector/laser/electro-absorption modulator. The team discovered that driving the modulator with an alternating current yielded a significant, low-frequency improvement in linearity over conventional voltage modulation.

In another paper, more than a dozen engineers at Bell Laboratories report on their 10-Gbit/sec transmission experiments using a monolithically integrated polyimide-free electro-absorption modulator/ distributed feedback laser grown by the selective-area epitaxy process. Because of low dynamic chirp, the group observed minimal excess distortion of the transmitted eye waveform.

Investigators at BNR Europe Ltd. and the University of Bath School of Physics claim to have time-resolved chirp measurements on integrated laser electro-absorption modulators. They maintain that system performance is improved with negative chirp, especially when the device is reflection sensitive.

Oki Electric Industry Co. engineers have developed a 10-Gbit/sec electro-absorption modulator module using a high-mesa ridge structure with an indium gallium arsenide phosphorus bulk absorption layer. They measured a polarization-dependent loss of less than 0.3 dB with a 20-dB signal attenuation.

In an invited paper, Masahiro Aoki and Hirohisa Sano of Hitachi Ltd. in Tokyo will describe their high-performance modulator-integrated light source fabricated by a bandgap energy control epitaxy process. They characterize the device with greater than 10-Gbit/sec speed, low chirp and controllable wavelengths for long-haul high-bit-rate wavelength-division multiplexer systems.

Also on Tuesday, S. Wagner at Bellcore will kick off the Subscriber Loop Networks session with a paper that focuses on the key technical challenges to delivering digital services over hybrid fiber/coaxial-cable networks, including both broadcast and two-way switched offerings.

Researchers from Bell Laboratories will cover a passive optical network based on a waveguide-grating router in which both downstream and upstream information signals are spectrally sliced. Another Bell Laboratories` team will describe the use of a single directly modulated and tunable distributed feedback laser that delivers mixed formatted signals in a wavelength-division multiplexer passive optical network, known as Rite Net.

Engineers at the NTT Interdisciplinary Research Laboratories in Japan have prototyped an optical main-distributing frame system using a fiber handling method that can crossconnect fibers and make connection routes for testing.

A team consisting of investigators at MIT Lincoln Laboratory and Digital Equipment Corp. have developed an interface for an all-optical network that uses simultaneous time slotting and frequency-division multiplexing. The interface provides connectivity to conventional networks carrying Sonet, fiber distributed data interface and ATM traffic.

Network topologies

Network topologies come under scrutiny in another Tuesday session. For example, France Telecom engineers have designed multilayer Fabry-Perot filters to structure an optical add/drop multiplexer in a wavelength-division multiplexer survivable ring network with spectral reuse. Another add/drop optical-filter design that is discretely tunable along equally spaced channels has been formulated by B. Glance at Bell Laboratories

E. Park and A. Willner at the University of Southern California have optically replaced the 8-bit header of a 1-Gbit/sec packet and simultaneously shifted the packet`s wavelength by 19 nm by modulating the probe laser only when the header bits required changing. In a dynamically reconfigurable wavelength-division multiplexer network, they obtained a receiver sensitivity of -25 dBm at a 10-9 bit-error rate using a 416-bit pattern.

Bell Laboratories` researchers will report on their successful operation of a subcarrier multiple-access passive optical network using multimode lasers with optical beat interference to 15 dB greater than the signal channel power.

A group of engineers at NTT Optical Network Systems Laboratories is covering a 40-Gbit/sec, 4-bit-long optical pattern matching circuit that uses fiber four-wave mixing.

Optical network design and operation are expounded at a Wednesday session. In one paper, engineers at the IBM T.J. Watson Research Center will present a commercial application of a 20-wavelength-division-multiplexer linked system known as Mux-Master. Other IBM engineers, in an invited paper, will show how a computer-aided-design tool can be used to satisfactorily obtain solutions to the complex tradeoff among network topologies, switches, wavelength allocations and routing procedures.

In another paper, a Bell Northern Research Ltd. team will assess the ability of wavelength-routed transport networks to bypass electronic switching equipment and how to quantify the potential equipment savings.

Researchers at Lincoln Laboratory and the Massachusetts Institute of Technology will recount their development of a network management subsystem for a wavelength-division multiplexer all-optical test bed. For a similar system, Siemens AG engineers will convey a means for efficient and compact operation and maintenance of high bit-rate streams.

Mitre Corp. investigators will analyze just-in-time switching and connect-confirm signaling schemes for an all-optical multiswitch network by using burst switching.

Multiwavelength networks

This popular subject is offered in a Thursday session. In one paper, a joint effort by Bellcore and Hughes Research Laboratories researchers will deal with the simultaneous transmission of subcarrier, multiplexer, multichannel FM-video; 3-GH¥digital signals; and ATM/Sonet multimedia services over 160 km of singlemode fiber. The system uses a cascade of six erbium-doped fiber amplifiers and five wavelength-division multiplexer crossconnects in a reconfigurable, multiwavelength, all-optical network test bed.

Engineers from Siemens AG and Deutsche Telekom will reveal their work on adding an all-optical network layer, which is based on optical frequency-division multiplexing with crossconnect and add/drop functions, to existing public telecommunications transport networks running SDH and ATM protocols.

A France Telecom group is proposing an experimental optical wavelength-division multiplexer ring network using an add/drop multiplexer based on a fiber grating filter. Another team from Alcatel Alsthom Recherche is reporting on a 4ٶ all-optical crossconnect that is capable of routing four multiplexed 10-Gbit/sec channels.

Engineers from Stanford University will examine packet-header subcarrier multiplexing and clock-recovery techniques in implementing an in-band control channel for an optical network.

Beyond 10 Gbits/sec

In a Thursday session, ultra-fast systems receive close observation. Researchers at BNR Europe Ltd. will detail 40-Gbit/sec transmission over 140 km of dispersion-shifted fiber with an optical sensitivity of -26.8 dBm and a power penalty of less than 1 dB.

Researchers at NEC Corp. will divulge optical clock extraction with only 0.1-ps excess jitter from 10-Gbit/sec data by synchronous injection mode-locking in a monolithic laser diode. q

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