Thanks, Don... it is interesting, like you say, although four years ago leaves one wondering how relevant the data is today. Internet time, third super-wave currents, and all. Quite impressive, though, in any event. Thanks.
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The following is this month's guest editorial in the December IEEE Communications Interactive on the subject of Multi-Wavelength Fiber Optic Communication by Michael R. Wang, assistant professor of electrical and computer engineering at the University of Miami.
I would be very interested in hearing comments from members here, concerning the author's viewpoints.
[Courtesy of Curtis Bemis on the CIEN Thread]
207.127.135.8
Note: The above link will also take you to a number of related articles on this subject.
Enjoy, FrankC.
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Multi-Wavelength Fiber Optic Communication
by Michael R. Wang
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During the past two decades, there has been rapid advancement in optical fiber communication technology. Reduction of single-mode fiber losses, the advent of erbium-doped fiber amplifiers (EDFAs), improved optical receiver sensitivity, and the development of high-speed semiconductor laser diodes have promoted the development of high-data-rate long-distance fiber optic communication networks with minimal or even no opto-electronic repeaters. To provide superior use of optical fibers, multiwavelength communication has been considered a promising technology that can greatly enhance fiber transmission capacity and network application flexibility.
Semiconductor laser-pumped EDFAs are now a realistic and practical method for providing direct low-noise amplification of broadband optical signals at 1.55 mm wavelength window without requiring opto-electronic conversion. The wide gain bandwidth of the EDFA (1.531.56 mm) and its low fiber propagation loss region (about 200 nm span around 1.55 mm) encourage the use of multiwavelength communication techniques for communication capacity improvement. With the development of high-speed semiconductor laser with narrow line width and close channel spacing, many wavelength channels can be placed in the EDFA gain bandwidth to facilitate multiwavelength communication in each fiber.
To effectively realize the multiwavelength fiber optic communication, there have been significant developments on network protocols as well as on hardware components. The multiwavelength network management is to provide efficient data transfer from transmitters to destination receivers without data stream collision at each routing node. There are several network protocols proposed to resolve network routing contention problems. The first article, written by Senior et al., provides an overview of the multiwavelength networking. This is an excellent article that gives basic understanding of the network protocols and requirements.
The hardware components for multiwavelength communication include fixed and tunable semiconductor lasers, tunable optical filters, fixed and tunable receivers, wavelength conversion devices, wavelength division multiplexers and demultiplexers, and add/drop routing elements.
Fixed transmitters and fixed receivers (FTFR), tunable transmitters and fixed receivers (TTFR), fixed transmitters and tunable receivers (FTTR), and tunable transmitters and tunable receivers (TTTR) are four basic techniques for the implementation of multiwavelength networks. Obviously, both fixed and tunable semiconductor lasers or laser arrays are critical components for the multiwavelength networks. Laser wavelength line width and wavelength channel separation determine the number of wavelength channels available to be inserted in the fiber amplifier's gain window. The second article, by Martin Zirngibl, summarizes recent development of compact-packaged multifrequency lasers at Bell Labs. Their performance has also been compared to well-known distributed feedback laser arrays that have already been deployed in many multiwavelength networks.
On the receiving ends both fixed and tunable receivers are important. The receivers are either fixed to receive a specific wavelength or allowed to be tuned to receive different wavelength signals. A fixed receiver can be implemented by using a passive wavelength demultiplexer or a passive optical filter with a receiver unit. A tunable receiver can be implemented by using a passive wavelength demultiplexer with an electronic selectable receiver unit. It can also be implemented by using a tunable optical filter with a fixed receiver unit. The electronic selectable receiver demonstrated faster wavelength channel selection than the tunable filter approach. The third article, by Frank Tong, provides an overview on such multiwavelength receiver and on receiver packaging. His article also details several types of passive wavelength division multiplexers and demultiplexers that can be used for the receivers.
Tunable optical filters are important for the tunable receivers mentioned above. They are also critical to dynamic network traffic routing. For example, they can be used to selectively add or drop particular wavelength channels from the multiwavelength network and to facilitate optical cross-connects. Key filter parameters include insertion loss, bandwidth, sidelobe, dynamic range, tuning speed, etc. The fourth article, by Sadot and Boimovich, provides an excellent overview of a variety of tunable optical filters for multiwavelength communication applications.
Converting channel wavelength from one to another is critical for wavelength routing. Used with a passive wavelength multiplexer router, the wavelength conversion can route a data signal to a different output port. It can also help reducing the data blocking probability in the network. All-optical wavelength conversion is preferred since it is fast. The fifth article, written by Nesset et al., provides a tutorial overview of the all-optical wavelength conversion using a semiconductor optical amplifier that is effective and compact.
Array-waveguide gratings (AWG) have been widely utilized for the implementation of multifrequency lasers, receivers, optical cross-connects, and passive and active WDM routers. The last article by McGreer details AWG's design and performance issues.
The success of this feature topic would not be possible without the motivation of the authors. I would like to express my appreciation and thanks to them for their valuable contributions and timely revision of their articles. I would also like to thank the reviewers and the editorial staff of IEEE Communications Magazine who helped to make this feature topic a reality.
Biography
Michael R. Wang is an assistant professor of electrical and computer engineering at the University of Miami. He received a Ph.D. in engineering from the University of California, Irvine. Prior to joining the University of Miami in 1995, he was a team leader in Photonic Devices at Physical Optics Corporation, where he played a leading role in the development of integrated optical devices, wavelength division multiplexers and demultiplexers, and optical interconnect components and subsystems. His current research areas include photonic devices, optical interconnects, and optical data storage. He has been a principal investigator and project manager in over 15 U.S.-government-sponsored SBIR, STTR, and university research programs. |
