Page 241 - Optical Communications Essentials

Constructing the WDM Network Puzzle

Constructing the WDM Network Puzzle 231

based on examining the characteristics of the optical signal is needed to verify
that an optical link is operating properly.
One means is to use a miniature spectrum analyzer to monitor power versus
wavelength at given points along an optical link. The resultant information of
signal power versus wavelength is useful for determining the optical signal-
to-noise ratio (OSNR), finding the absolute wavelength of a specific channel,
and verifying that the channel spacing is adhering to the ITU wavelength spec-
ification.
The points along a link where this monitoring may be done include at the
laser transmitters, at the output of optical amplifiers, at an add/drop multi-
plexer, and immediately following a demultiplexing device. Chapter 18 presents
further details on these functions.

13.5. Summary
The discipline of wavelength division multiplexing has undergone dramatic
changes in the past several years. New passive and active components are
appearing steadily, and different wavelength combining methods are being
examined. The technology has moved from multiplexing a few widely spaced
wavelengths onto a fiber to dense WDM in multiple bands, coarse WDM rang-
ing from the O- through the L-band, and recently hyperfine WDM where 320
wavelengths spaced 12.5GHz apart are packed into a narrow spectral band. The
future holds more excitement as researchers examine components and signal
processing techniques needed for implementing wavelength channels spaced
6.25GHz apart.

Further Reading

The following are some general sources for further study on basic aspects of
optical fiber communications and WDM applications.

1. G. Keiser, Optical Fiber Communications, 3d ed., McGraw-Hill, Burr Ridge, Ill., 2000.
2. R. Ramaswami and K. N. Sivarajan, Optical Networks, 2d ed., Morgan Kaufmann,
San Francisco, 2002.
3. A. Gumaste and T. Antony, DWDM Network Designs and Engineering Solutions, Prentice Hall,
Upper Saddle River, N.J., 2003.
4. J. Hecht, Understanding Fiber Optics, 4th ed., Prentice Hall, Upper Saddle River, N.J., 2002.
5. I. P. Kaminow and T. Li, Optical Fiber Telecommunications, IVA and IVB, Academic Press,
New York, 2002.
6. K. Liu and J. Ryan, “All the animals in the zoo: The expanding menagerie of optical com-
ponents,” IEEE Communications Mag., vol. 39, pp. 110–115, July 2001.
7. H. Shakouri, Sr., “Temperature tuning the etalon,” Fiberoptic Product News, vol. 17, pp. 38–40,
February 2002.
8. C. Duvall, “VCSELs make metro networks dynamic,” WDM Solutions, vol. 2, pp. 35–38,
November 2000.
9. J. Chon, A. Zeng, P. Peters, B. Jian, A. Luo, and K. Sullivan, “Integrated interleaver technology
enables high performance in DWDM systems,” Proc. National Fiber Optic Engineers Conference
(NFOEC), pp. 1410–1421, September 2001.

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