Page 170 - Optical Communications Essentials

Passive Optical Components

160 Chapter Nine

thin films separated by cavities. For a single cavity the transmission function
has a sharply peaked passband with sides that roll off smoothly. As the number
of cavities increases, the passband of the filter sharpens up to create a flat top
for the filter, which is a desirable characteristic for a practical filter. Thin-film
filters are available with passbands from 50GHz and higher. Table 9.5 lists
some operational characteristics of commercially available 50-GHz multilayer
dielectric thin-film filters for use in fiber optic communication systems.
A grating is an important element in WDM systems for combining and sepa-
rating individual wavelengths. Basically it is a periodic variation in a material,
which reflects transmitted light depending on the wavelength. One embodiment
is to create a fiber Bragg grating (FBG) in the core of an optical fiber. Table 9.6
lists some operational characteristics of commercially available 25-, 50-, and
100-GHz fiber Bragg gratings for use in optical communication systems.

Further Reading

1. J. J. Pan, F. Q. Zhou, and M. Zhou, “Thin films improve 50-GHz DWDM devices,” Laser Focus
World, vol. 38, pp. 111–116, May 2002 (www.laserfocusworld.com).
2. F. Chatain, “Fiber Bragg grating technology passes light to new passive components,” Lightwave,
vol. 18, pp. 186, 190–191, March 2001 (www.light-wave.com).
3. C. Zhou, P. Chan, J. Yian, and P. Kung, “Fiber Bragg gratings stretch metro applications,” WDM
Solutions, vol. 4, pp. 41–43, May 2002 (www.wdm-solutions.com).
4. S. DeMange, “Thin-film filters give flexibility to OADMs,” WDM Solutions, vol. 4, pp. 31–34,
June 2002 (www.wdm-solutions.com).

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