Page 282 - Fiber Bragg Gratings

6.3 The Michelson interferometer band-pass filter 259

band period is now chirped, since the variation in the detuning is no
longer constant close to the phase-matching wavelength.
Figures 6.28 and 6.29 demonstrate the effect of the counter-chirp of
the gratings for the more general case of dissimilar length gratings. At
the top of Fig. 6.28 is shown a schematic of the third combination for the
chirped gratings (C) and the relative positions, orientations and lengths

Output of asymmetric Michelson interferometer with 10nm, 5 &10mm long oppositely
chirped gratings (0.3448 mm path difference)

Figure 6.28: Above the chart is shown the arrangement of the gratings (C)
used in this simulation of the asymmetrically placed grating Michelson interferom-
eter BP with identical chirp bandwidth but dissimilar lengths (5 and 10 mm).
Notice the chirp in the period of the pass bands. The reflectivity of one of the
gratings is also shown.

Figure 6.29: The band-pass response with a 3.448-mm path difference.