Page 442 - Fiber Bragg Gratings

9.3 Phase and temporal response of Bragg gratings 419

Figure 9.11: The reflectivity and phase of a 4-mm-long unapodized grating
4
with a refractive index modulation amplitude of 4 X 10~ .

Typically, the accumulated phase for a 4-mm-long grating is a few
tens of radians, as shown in Fig. 9.11.
The group delays of the two gratings used for Fig. 9.9 are shown in
Fig. 9.12. The strong dispersion at the edges of the band stop limits the
useful bandwidth of a band-pass filter, especially in high-speed applica-
tions [15,16]. In Ref. [16] asymptotic expressions may be found for the

Figure 9.12: Dispersion of 4-mm-long unapodized (U) and apodized (A) grat-
ings.