Page 250 - Fiber Bragg Gratings

Chapter 6

Fiber Grating Band-pass

Filters

Let the band pass. .

For many applications, the transmission characteristics of a fiber Bragg
grating are really the wrong way around: it is a band-stop rather than a
band-pass filter. For example, tuning a radio enables the selection of a
channel, not the rejection of it from a broad frequency spectrum. However,
a Bragg grating works quite in reverse, and therefore cannot be easily
used for channel selection. Optical transmission systems also require a
"channel-dropping" function, in which a channel is selected from a large
spectrum of designated channels. These optical channels are on a coarse
grid of 100 GHz (multiples and submultiples of), which is currently being
debated. A system based on wavelength or frequency sliced channels is
a logical one and will prevail in future telecommunications networks. The
advantage of such a standardized system is not in doubt, only the alloca-
tion of the channels, which is a matter for discussion by international
standards committees around the world. In view of the future worldwide
integration of telecommunication services, it is only a matter of time
before an industry standard emerges.
The immediate question that springs to mind is: Will fiber gratings
play a role in emerging systems, given that their function is not the one
naturally desired in a majority of application in filtering? The answer to

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